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a-Peroxyamines.

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Volume 12 - Number 10
October 1973
Pages 783 - 868
International Edition in English
a-Peroxy amines
By E. G. E. Hawkins[*]
a-Peroxyamines contain the group
I
>N-C-0-0--,
I
which may also be incorporated
into a ring. Numerous compounds of this type are accessible, inter a h , from ketones,
hydrogen peroxide, or alkyl hydroperoxides and ammonia, as well as by autoxidation
or photo-oxidation of amines or imines. Apart from decomposition reactions, the chemistry
of these compounds is characterized by interesting cyclizations to give lactams, h i d e s ,
oxaziridines, tetroxanes, etc.
1. Introduction
Although isolated examples of x-peroxyamines have been
described in the literature, either as definite compounds
or as possible intermediates in oxidation reactions, over
a number of years, a systematic study of these substances
(including novel cyclic 1,2,4-dioxazolidines) has been
pursued only recently.
Our work in this field originated from the discovery of
the new compound 3,3 ;5,5-bis(pentamethylene)-l,2,4-dioxazolidine ( I ) during a study of the reaction of cyclohexanone, ammonia, and hydrogen peroxide, in the presence
of tungstate catalysts, reported to give cyclohexanone
oxime (for references seel41), and its decomposition to
caprolactam (with bases) and 1 1-cyanoundecanoic acid
(on pyrolysis)-which on hydrogenation provided 12aminododecanoic acid, the monomer of Nylon 12. Extension of this work to the related peroxyamines was a
natural sequel.
[*] Dr E G. E. Hawkins
BP Chemicals International Ltd.
Great Burgh
Yew Tree Bottom Road
Epsom. Surrey (England)
Angrw. Chrm. infernur. Edit.
Vol. 12 ( I Y 7 3 ) 1 No. 1 0
This review is intended to describe the preparation and
reactions of a-peroxyamines where the peroxy group is
a to nitrogen, but does not include cc-peroxyhydrazines
nor a-peroxyazo compounds, and omits references to oxygenation reactions where 2-peroxyamines are probable
intermediates but where their isolation has not been possible.
2. N-Unsubstituted a-Hydroperoxyamines
[R'R2C(OOH)NH2]
2.1. Formation
Early work with these compounds is sparse. Schenck['I
has stated, without detail, that they are formed by photooxidation of amines, but their isolation would have been
difficult in view of the ease with which they undergo decomposition and further reaction under the experimental conditions. Small amounts of a-hydroperoxycyclohexylamine
(2) were isolated during photo-oxidation of cyclohexylamine"], but the major products were the amine-hydrogen
peroxide adduct, and imines and amides, all of which
are probably produced cia the a-hydroperoxyamine.
The presence of (2) was detected, by thin-layer chromatography, in the products of ozonolysis of bis(cyclohexy1idene) in the presence of ammoniaF3],but was identified
783
only by means of the N-benzoyl derivative of its dehydration product, 2-pentamethyleneoxaziridine (3).
3. N-Monosubstituted a-Hydroperoxyarnines
[R 'R2C(OOH)NHR3]
3.1. Formation
However, r-hydroperoxycyclohexylamine ( 2 ) may be prepared as a solid in high yield by direct reaction of cyclohexanone, hydrogen peroxide (molar ratio L'U. 1 : I ) , and
ammonia'"'. It is unstable at room temperature, particularly when impure, and easily reverts to cyclohexanone,
with loss of ammonia; storage for several weeks at -2O:'C
is possible. The corresponding x-hydroperoxyamines were
similarly obtained, in varying yields, from other cyclic
Compounds of this class have been obtained by reaction
of imines with ethereal['] or
hydrogen peroxide
or by ozonolysis of olefins in the presence of a primary
arnineC31.
R1R2C=NR3 + H,O,
* *
\
/"
R1R2C@02'
/
NHR3
R'R~C,
'M
M HH
+ R3NH2
Hydroperoxides have been isolated from oxygenation products of certain cyclic amines, e.g. ( 7 ) , R=O-OH, from
(7), R=Ht9], and (8),R=O-OH from (8),R=H["],
whilst photo-oxidation of hexamethylphosphoramide gave
rise to the unstable ( Y ) [ l l l which decomposed to give
formaldehyde or formic acid.
ketones (3- and 4-methylcyclohexanone, cycloheptanone,
cyclododecanone, and dihydrois~phorone)[~~,
but none was
isolated from acycliccarbonyl compounds[61.The P,y-unsaturated ketone isophorone yielded the P,y-epoxy-4-hydroperoxyamine ( 4 ) ria the epoxide.
N-!
2.2. Reactions
The r-hydroperoxyamines reacted with carbonyl compounds to give moderate yields of 1,2,4-dioxazolidinescyclic peroxyamines-(5)[". '1. However, the products frequently also contained symmetrical cyclic peroxyamines
through reaction of hydrogen peroxide and ammonia. produced by breakdown of the hydroperoxyamine, with the
more reactive of the carbonyl compounds present.
Oxidation of 3 ~-hydroxysolanide-I6(N)-eninium
perchlorate with alkaline hydrogen peroxide provided the cc-hydroperoxyamine ( I O ) , which could be reconverted to the starting compound by dilute perchloric acid in methanol[121.
(51
COCH,
r-Hydroperoxycyclohexylamine (2) reacted with: (i) ferrous sulfate to yield cyclohexanone with some hexanamide
and hexanoic acid ; (ii) ferrous chloride to give cyclohexanone, a)-chlorohexanamide, and w-chlorohexanoic acid;
and (iii) sodium tungstate or tungstophosphoric acid to
provide cyclohexanone oxime. Pyrolysis of (2) at 450 to
500 'C/150 torr gave products similar to those derived
from 3,3;5,5-bis(pentamethylene)-l,2,4-dioxazolidine( 1 )
(Section ELI), whilst attempts at acetylation yielded a solid
peroxide, thought to have the structure (ti), which decomposed to cyclohexanone and acetamide at higher temperatures.
784
A number of r-hydroperoxyamides have been produced,
either by autoxidation [ e .g. ( I I ) from caprolactam["]],
photooxidation [ I P . ~ . (13) from (12)[141], irradiation [e.g.
( 1 4 ) from thymidine''51], or reaction of hydrogen peroxide
withenamines [ ~ . g . ( 1 6 ) f r o m ( 1 5 ) ~(~1~8~) from
];
(20) from ( l Y ) , R = H , CH3[lg1;and (22) from (21),
R=CH,,C6H,CH,'191].
Anqrw. Chem. intemar. Edit.
Vol. 12 ( 1 9 7 3 ) 1 No. 1 0
P
W
CII,
CH,
(151
1161
H
R
= Cyclohexyl
oo
t
R-NHCHO
The a-hydroperoxylactam ( I I ) was reduced by hydriodic
acid to the w-formyl amide (28)["1, and converted into
and
a 1,2,4,5-tetroxane (29) by 70-80 70sulfuric
into adipimide ( 3 0 ) by cobalt-catalyzed decompositionl'-'].
CONH2
C C H O
(211
(22)
Reaction of hydrogen peroxide and ammonia with ethyl
levulinate or levulinamide yielded both the hydroperoxylactam (23) and peroxydilactam (24)[61.
Hydroperoxide (13) is reduced by potassium iodide/acetic
acid to the corresponding diol which, in polar solvents,
undergoes ring opening to yield [31)['4'.
3.2. Reactions
Many a-hydroperoxyamines, when heated in a solvent['* 31
or treated with acidslx1 ( e .9. acetic acid/acetic anhydride),
are converted into the corresponding oxaziridine; N-cyclohexyl- 1 -hydroperoxycyclohexylamine (25) is converted
in to N-cyclohexylcaprolactam (and N-cyclohexylidenecyclohexylamine) by lithium chloride in methanol, presumably via the oxaziridine (26)"I.
With alkali ( 2 5 ) gives the corresponding imine by loss
of hydrogen peroxide, and with acidified ferrous sulfate
it is partly converted into N-cyclohexylhexanamide and
N,N'-dicyclohexyldodecanamide[81,products similar to
those from treatment of the corresponding oxaziridine
(26) with ferrous
Reaction of ( 2 5 ) with formaldehyde gives the unstable 1,2,4-dioxazolidine ( 2 7 ) , which
decomposes on storage at room temperature to form cyclohexanone and N-cyclohexylformamide~81.
A t i y i w Chrm mfernar. Edrr
i
Vi,l 12 ( l Y 7 3 ) / No. 10
Thermal decomposition of (16) led to the imide [32)
by loss of methanol, and further treatment with water
gave an anhydride ( 3 3 ) and methylamine[lhl.
4. N-Substituted u-Hydroperoxyimines
[R'R2C(OOH)N=R3]
4.1. Formation
Photosensitized oxygenation of certain substituted pyrroles
(34) [(a) R 1 = R Z = R 3 = R 4 = C6 H 5 lzzl; (b) R ' = R 4 =
785
C 6 H 5 , R 2 = R 3 = H ; (c) R1=RZ=R4=(CH3),C, R 3 = H ;
(d) R1=R4=(CH3)3C, R 2=R3 =H[23]1 has produced
the corresponding 2-hydroperoxy-2 H-pyrroies (35);
the tetraphenyl compound (35 u ) , together with the epoxyhydroperoxide ( 3 6 ) and a number of other products, was
R2
R
-
R3
H
R2 R3
N
(45).
(340)
H5c65:625
BR4
R1
alkoxy)-3,4-epoxytetraphenylpyrroline( 4 4 ) and the amide
(4'0, R
= H, Alkyl
O-OH
H5C6
'N
O-OH
(45)
also obtained by treatment of tetraphenylpyrrole ( 3 4 a )
with hydrogen peroxide[24'. Similar photo-oxidation of
2,4,5-triphenylimidazole (lophine)[25,261,
or reaction of
dilute hydrogen peroxide with the 2,4,5-triphenylimidazyl
radical[251,gave rise to a related a-hydroperoxyimine
( 3 7 ) ,and photo-oxidation of 1-hydroxytetraphenylpyrrole
(38) provided an x-hydroperoxynitrone (39)L2'1. Autoxi-
gH5
X*CH5
H5C6
N
O-OH
OH
60
1-38]
1-39)
H5C6.
CsH5
(46)
(471
Strong acids convert (35 a) into hydrogen peroxide and
a salt of the corresponding hydroxy compound ( 4 6 ) ,
whereas strong bases afford the lactam ( 4 7 ) , which is
also formed by rearrangement of ( 4 6 ) on heating. Treatment of ( 3 5 a ) with hydrogen peroxide in neutral solvents
(dioxane or ethanol) yields largely the epoxide ( 3 6 ) , but
in acetic acid ring-opening occurs with production of (45)
and (48).
Similar products to ( 4 8 ) , on storage, and ( 4 6 ) and ( 4 7 ) ,
on reduction with potassium iodide/acetic acid, have been
obtained from the 2-hydroperoxy-2,5-di-trrt-butyl- and
2,4,5-tri-tert-butyl-2 H-pyrroles (35d) and (35 c ) respecti~eIy[*~].
dation of 1,3,4,7-tetramethylisoindole in benzene/ether at
room temperature led to the formation of the hydroperoxide (40) [281.
The anticipated formation of a bicyclic peroxyamine (42)
from the reaction of 2,5-hexanedione ( 4 1 ) with hydrogen
peroxide and ammonia did not occur; instead, the hydroperoxypyrroline (43) was obtained and intramolecular
cyclization may have been prevented by steric hindrance"].
The hydroperoxypyrroline (43) was converted into 2,5dimethylpyrrole by sodium methoxide, 2,5-hexanedione
by ferrous sulfate, and a mixture containing these two
compounds on pyrolysis['!
5. N-Unsubstituted a-Alkylperoxyarnines
[R'R2C(OOR3)NH2]
5.1. Formation
H3C
(421
L hy HC&OH
3
(43)
Treatment of cyclohexanone with ammonia and tert-butyl
hydroperoxide gave an equilibrium mixture which contained 1 -tert-butylperoxycyclohexylamine ( 4 9 ) ; distillation of the product led to some decomposition, with loss
of tert-butyl hydroperoxide. Spectroscopic examination of
the higher-boiling reaction products suggested that the
peroxyimine ( 5 0 ) was also formed by further reaction
of ( 4 9 ) with cyclohexanone. The l-tcrt-butylperoxycyclohexylamine ( 4 9 ) provided normal amine derivatives (52 )
4.2. Reactions
A
The reactions of 2-hydroperoxytetraphenyl-2H-pyrrole
( 3 5 a ) (R' = R 2 = R 3 = R 4 = C 6 H s ) have been studied in
depth'". 24. 281. Thermal decomposition of neat (35 a )
brings about formation of tetraphenylpyrrole (34 a ) and
liberation of oxygen. A similar reaction occurs when heating is carried out in nonpolar solvents, but in polar solvents
(e.y. alcohols) the major products are 5-hydroxy(or 5786
Angew. Chem. internat. Edit. J Vol. 12 ( 1 9 7 3 ) J
No. I0
with phenyl isocyanate, acetyl chloride, benzoyl chloride,
ethyl chloroformate, p-toluenesulfonyl chloride, and tertbutyl h y p o c h l ~ r i t e [ ~ ~ l .
Replacement of tert-butyl hydroperoxide by cumene hydroperoxide gave a crude product containing the peroxycyclohexylamine corresponding to ( 4 9 ) , but although this
Pyrolysis of the N-acetyl derivative (51 1, R =CH,CO,
led to a complex mixture of products including acetone,
tert-butanol, cyclohexanone, acetic acid, hexanoic acid,
acetamide, a-methylhexanenitrile
incorrectly
as a-methylpentanenitrile) and N-acetylhexanamide, as
well as smaller amounts of lower molecular weight com-
+ CH&N
could not be distilled without decomposition its presence
was proved by formation of a crystalline phenylurea derivative
N o similar a-alkylperoxyamines could be isolated when
starting with acyclic ketones (2-butanone and 3-pentanone), and acyclic aldehydes (acetaldehydeand n-butyraldehyde) gave products thought to be largely the diperoxyamines (52), which on distillation tended to lose a molecule
of trrt-butyl hydroperoxide with formation of imines
ccH.
CONHCOCH,
6
+ CH3C02H
pounds. The main products are formed in free-radical
reactions.
Reaction of the N-acetyl derivative with sodium methoxide
proceeded oin N- 1-cyclohexenylacetamide to cyclohexanone and acetamide.
N-Chloro-frrt-butylperoxycyclohexylamine ( 5 1 ), R =el,
also lost tert-butyl hydroperoxide on treatment with
sodium methoxide to give N-chlorocyclohexylideneimine
and thence, by a Neber reaction, 2,2-dimethoxycyclohexylamine,
( 5 1 ) . R = C1
(53)[291.
+ (CH3),COOH
NaOCll,
5.2. Reactiom
CH30H
Decomposition of ( 4 9 ) by sodium methoxide led to evolution of ammonia and formation of cyclohexanone, whereas
pyrolysis at 45&550"C gave cyclohexanone, acetone,
unsaturated and saturated C6 amides, a C , branched amide
and traces of nitriles and acids. This thermal decomposition
evidently involves both reconversion to cyclohexanone and
tert-butyl hydroperoxide and homolytic scission of the
0-0 bond, followed by ring opening and methylation
of 1,5-rearranged radicals:
CONH,
CN
-+ C C H ;
CEzrHz
CH,'
6. N,N-Disubstituted a-Alkylperoxyamines
[R 'R2C(OOR3)NR4Rs]
6.1. Formation
When tert-butyl hydroperoxide was heated with dimethylaniline in the presence of heavy metal ions N-tert-butylperoxymethyl-N-methylaniline was produced in high
yieldc3'].
+ (CH,),CO
+
CONH,
CE;YHz
C C H ,
Anyew. Chem. inturnat. Edit. / &)/. 12 ( I Y 7 3 ) ! No. I0
CONH,
A number of l-tert-butylperoxy-2-aryl-1,2,3,4-tetrahydroisoquinolines (54) have been similarly prepared by treat787
ment of the corresponding 2-aryltetrahydroisoquinoline
with rurr-butyl hydroperoxide and cuprous chloride in
benzener3 '1.
(54)
N,N-Disubstituted r-peroxyamines have also been synthesized in good yields by treatment of a secondary amine
with formaldehyde and a hydr~peroxide[~']
or hydrogen
RzNH + HCHO
RzN-CHzOH
K'O-011
R,N--CH,-O-OR'
bis(N-aryltetrahydro-1-isoquinolyl) peroxides (57jC3'1,
whereas the N-alkyl- and 1,2-disubstituted compounds did
not autoxidize[38J.Of the tricyclic amines examined, the
N-substituted 23-dihydro- 1H-benz[d,e]isoquinolines ( 5 8 )
did not react under similar conditions,whereas both N-substituted 5,6-dihydrophenanthridines (59)[38] and N-aryl6.7-dihydro-5H-dibenz[c,e]azepines (61
gave the symmetrical peroxides ( 6 0 ) and ( 6 2 ) respectively.
The mixture of amine and formaldehyde may be replaced
by the preformed N-hydroxymethylamine, and the less
reactive amides undergo a similar reaction in the presence
of acids[321.
H2N-CD-NHz
+
2 HCHO + 2 (CH,),C-OOH
+
Similarly, a-hydroxymethyl peroxides and primary or
secondary amines yield ct-pero~yamines[~~].
A number of symmetrical peroxyamines of type (55 j were
also produced by autoxidation of tertiary aromatic amines
in the presence of an i n i t i a t ~ r [ ~and
~ . ~it~was
] , suggested
that the nonisolated a-hydroperoxyamines, e. g. ( 5 6 j , were
intermediates.
Similar symmetrical compounds have been obtained by
ozonization of tertiary aromatic amines at low temperatures in nonpolar solvents, with a suggested mechanism
involving initial attachment of the ozone to the nitrogen
Higher yields of these symmetrical peroxyamines, (57)
and (62), were obtained by reaction of hydrogen peroxide
with the corresponding dihydroisoquinolinium (or azepinium) bromide ( 6 3 ) . A similar type of reaction, with
N-methyl-6,8-dinitroquinolinium chloride, had previously
been used for obtaining crystalline derivatives from a
number of primary, secondary, and tertiary hydroperoxides["OI, whilst pseudo-bases [e.g. ( 6 4 ) and ( 6 5 ) , where
R = H ] may also be converted into peroxides [ ( 6 4 ) and
( 6 5 ) , where R =OR'] by treatment with hydroperoxides
(RIOOH)[~~)I.
It was found that benzene solutions of N-aryl-substituted
tetrahydroisoquinolines, on shaking with oxygen in UV
light, were converted into the corresponding crystalline
788
Anqvw Chem. internat. Edir. 1 Vol. 12 (1973)
i NO. 10
A related synthesis of x-peroxy-N-acyl (or N-sulfonyl)
amines, r.g. (66), involves the reaction of N-acyl- (or
N-sulfonyl-)N-vinylamines with tertiary alkyl hydroperoxides or hydrogen peroxide in the presence of acid catalysts
(S02CIzor S0Cl2) at low temperatures[18.411;N-vinyllactams give the peroxides (67), (681, and ( 6 9 ) .
of formic acid and hydrogen on heating bis(hydroxymethyl) peroxide[441).
A r N - C Hz-O-(3CHz-NAr
I
R
(55)
k
-.
2 ArN-CHO + II,
I
K
Base-catalyzed decomposition of the peroxides derived
from primary or secondary hydroperoxides and N-methyl6,8-dinitroquinolinium chloride (P. y. in pyridine) proceeds
by the normal Kornblum-De La Mare mechanism[4s1
to give the corresponding q ~ i n o l o n :e ~ ~ ~ ~
R3
H,C-CH-kH-C
CH,
Peroxides ( 5 7 ) and (60), when heated, disproportionated
into pseudo-bases and la~tams[~'."J.
H3
The enamines derived from cyclic ketones and cyclic
secondary amines (morpholine or piperidine) react with
ethereal hydrogen peroxide to give symmetrical x,a'-diamino peroxides'421, e.g. (70), although use of more hydrogen peroxide gives rise to the intermediate a-hydroperoxyamine (71)L431.
Pyrolysis of the r-tevt-butylperoxyamines ( 7 2 ) . as well
as their reaction with sodium methoxide, gave mainly
the corresponding imine (by loss of trrt-butyl hydroperoxide), although the thermal decomposition of N-ethyl- 1 -tcwtbutylperoxycyclohexylamine provided a product containing N-ethylamides indicative of homolytic fission of the
peroxide bond [*I.
H3C-CH-NH-CH-CH,
(CH,),Cd
bOC(CH,),
(521, R
The reaction of cyclic ketones or acyclic aldehydes (but
not acyclic ketones) with primary amines and rerr-butyl
hydroperoxide also yielded x-peroxyamines ( 7 2 ) ; the
lower-molecular-weight products were stable to distillation
but the higher-boiling homologs decomposed into the corresponding imines[*].
R'R'CO
+ R3NHz + (CH,),C-O-OH
+
YnO('l I)
= CH,
H,C-CO-NH-CH-CH,
I
OCH,
( 73)
+ (CHJ3COH
Reaction ofthediperoxyamine ( 5 2 ) , R =CH3, with sodium
methoxide gave mainly the a-methoxyamide ( 7 3 ) , as well
as acetamide: evidently, Kornblum-De La Mare reaction
occurred at one of the peroxide systems whereas in the
second simple replacement of the tert-butylperoxy group
by methoxyl took
6.2. Reactions
7. N-Substituted a-Alkylperoxyimines
[R R2C(OOR3)N=R4]
The symmetrical peroxides of type (55) were easily converted back into secondary amine, formaldehyde, and hydrogen peroxide by acids'331, but, surprisingly for diprimary peroxides, are reported to be stable to alkali. They
may be hydrogenated to the corresponding dialkylanilines,
and on thermal decomposition in toluene yield an N-alkylformanilide and hydrogen (comparable with the production
Autoxidation of the radical ( 7 4 ) , produced by reaction
of 2,3,4,S-tetraphenylpyrrole( 3 4 ~ with
)
lead dioxide, led
to the formation of the peroxide ( 7 5 ) , easily reduced to
the hydroxypyrrole ( 4 6 ) by hydriodic
The same peroxide ( 7 5 ) was obtained (in 20% yield)
during electrochemical oxidation of tetraphenylpyrrole in
the presence of sodium carbonate and air146J.
Angrrc Chrm. internat. Edit.
'
1 Vol. 12
( 1 9 7 3 ) i No. I 0
789
(344
heptanone, 2-, 3-, and 4-methylcyclohexanone, isophorone,
and dihydroisophorone, and the peroxyamines formed,
sometimes solid, could all be distilled without decomposition under reduced pressure. In those cases where the intermediate a-hydroperoxyamine (Section 2.1) could be isolated, further reaction with the ketone gave the cyclic
compounds ( g o ) , also formed from the corresponding
bis(1-hydroxyalkyl) peroxides and ammonia, e.g. ( I )
from (81).
( 74)
Oxidation of 2,3,4-trimethylpyrrole by hydrogen peroxide
in pyridine gave mainly the lactam ( 7 6 ) , but a by-product
peroxide (previously describedf4']) was assigned the structure ( 7 7 ) [ 4 8 Jhowever,
;
it seems more likely that this peroxide was ( 7 8 ) with either R1=CH3, R 2 = H or R 1 = H ,
R2=CH3.
Unsymmetrical 1,2,4-dioxazolidines (83) [see also (5 )]
could be obtained from a-hydroperoxyamines and a different carbonyl compound, although yields were often poor
and the product contaminated with one or both of the
symmetrical dioxazolidines. Presumably reaction proceeded uia cyclization of the a-hydroperoxyimine, and the
possibility of the formation of such intermediates by autoxidation (or photo-oxidation) of the corresponding imine
( 8 4 ) can be envisaged.
Reaction of the 2,4,5-triphenylimidazyl radical with a tertiary hydroperoxide (tert-butyl or cumyl) gave the corresponding 4 - p e r o ~ y i m i d a z o l e ~and
~ ~ ~ ,related chemiluminescent peroxides were obtained with phenyl replaced
by other aryl groups[49!
8. 1,2,CDioxazolidines
8.1. Formation
Earlier work on the production of these cyclic peroxyamines appears to have been limited to the photo-oxidation
of 1,2,3-triphenylisoindole,leading to high yields of the
compound ( 79)r5O1.
Recently it has been found that aldehydes and ketones
(both acyclic and cyclic), when treated with ammonia and
hydrogen peroxide, give rise to symmetrical cyclic peroxyamines (1,2,4-dioxazolidines) (80) [4-61.The carbonyl compounds used included acetaldehyde, n-butyraldehyde, acetone, 2-butanone, cyclohexanone, cyclopentanone, cyclo-
However, in general, attack of oxygen occurs at the methylene (or methine) group ci to carbon of the C=N
Exceptions to this generalization are imines having the
methylene (or methine) group
to nitrogen activated,
e.g., by aryl groups (cf. Section 4.1); thus, when R'=aryl
and R Z= alkyl or aryl, autoxidation (or photo-oxidation)
at low temperatures (0 to -20°C) led to the production
of 1,2,4dioxazolidines (83), R3, R4 = -(CH&--,
in
good
Oxygenation of the imine (84),
R ' = R Z = R 3 = R 4 = C 6 H 5 , was extremely slow, and under
forcing conditions the products obtained (benzophenone
and benzanilide) were those expected from decomposition
of the corresponding peroxyamine.
8.2. Reactions
The most detailed reaction study was carried out with
3,3;5,5-bis(pentamethylene)-l,2,4-dioxazolidine( I ) , but
the behavior of the other members of this class of compounds is very similar.
xNxl
R'
R'R'CO
+ HzO2 + NH,
--t
+ HzO
R2 0-0 R2
790
The amine group may be acetylated (by acetyl chloride)
chlorinated (by tert-butyl hypochlorite), methylated (by
methyl icdide/silver carbonate), or converted into a phenylurea (by phenyl isocyanate). Catalytic hydrogenation of
( I ) leads to cyclohexylamine or cyclohexanone, whereas
treatment with aqueous acids or bases gives cyclohexanone.
Anyew. Chum. internur. Edit.
,
i Vol.
I2 (1973) 1 No. I0
With formic acid or acetic acid the cyclohexanone is accompanied by some caprolactone (through Baeyer-Villiger
reaction) and ammonium formate or acetate. Treatment
of ( I ) with warm ferrous sulfate afforded low yields of
hexanamide and dodecanediamide, whereas ferrous chloride and cuprous chloride gave o-chlorohexanamide and
heating with copper naphthenate (catalytic amount) led
to 5-hexenamide[''.
The reactions of ( I ) which were of the greatest interest
were its decomposition by certain bases and its pyrolysis.
When heated in methanolic solution with sodium methoxide or phenoxide, an alkali-metal hydroxide, or lithium
chloride or bromide, the peroxyamine was converted in
high yield into caprolactam and cyclohexanone. The use
of other alkoxides, sodamide in benzene, or organic bases
( e .9. amines) gave variable and often low yields of caprolactam, and the by-products included 24 1-cyclohexenyl)cyclohexanone, hexanamide, 5-hexenamide, and octahydroacridines. Formation of 9-alkyl-l,2,3,4,5,6,7,8-octahydroacridines increased when higher alkoxide/alkanol systems were
used, and they were then accompanied by cyclohexanol;
presumably the greater activity of such alkoxides as cata-
1
lysts in bringing about Oppenauer-Ponndorf oxidationreduction reactions leads to such products.
RCHO + 2
ooa
0
0
CHR
Nil,
ll01
R
Angew. Chrm. inrrmut. Edit. ,I k/.12 l l Y 7 3 ) J N o . 10
Themechanism of formation of caprolactam and cyclohexanone probably involves nucleophilic attack of the methoxy-ion at the spiro-carbon site; removal of hydrogen
from the imino group is not involved since N-methyl-l,2,4dioxazolidine, under similar conditions, yields cyclohexanone and N-methylcaprolactam.
=
,7
0
0
+
oo
Thermal decomposition of ( I ) in the liquid phase gave
a complex mixture of products, including cyclohexanone,
caprolactam, and C1 compounds, whereas pyrolysis in
the vapor phase at 350-6OO'C under reduced pressure
gave ca. 60% yields of C l z compounds together with
caprolactam (ca. 20%) and cyclohexanone (<30%). The
I
CN
(89)
nature of the C l z compounds varied with the temperature
and residence time; at 3 5 W O O ' C the major product
was decanedicarboximide (85), and at higher temperature
1I-cyanoundecanoic acid (86). By-products, in minor
amounts, included the monoamide of dodecanedioic acid,
dodecanediamide, dibutylsuccinimide (871, 2-butyI-7cyanoheptanoic acid (a#), 7-cyanoundecanoic acid (8Y),
hexanamide, and a compound thought to be I-hydroxy-Nhexanoylhexanamide [ 90), which dehydrates to 5-butyI-2pentyl-4-oxazolinone (91 ) on distillation; the formation
of several of these C I by-products involves 1,5-radical
rearrangements.
Other symmetrical cyclic peroxyamines derived from cyclic
ketones behaved in a similar fashion on reaction with
791
sodium methoxide and on pyrolysis, although where isomeric lactams or cyano-acids were possible by rearrangement in two ways both were present in the p r o d u c t ~ [ ~ J .
L'nsymmetrical 1,2,4-dioxazolidines underwent base-catalyzed and pyrolytic decompositions to give mixtures of
ketones, lactams, and cyano-acids.
+
eo+06
amide on treatment with triethylamine, it afforded a
moderate amount of caprolactam on addition to a solution
of lithium chloride in boiling methanol[4].
9. Miscellaneous Cyclic Peroxyamines
and -imines
The addition of hydrogen peroxide to enamines to form
3-peroxyamines has already been mentioned (Section 6.1 1
However, the unsymmetrical dioxazolidines ( 8 3 j , R '
and/or R2=aryl; R3,R4=-(CHz)5--, obtained by imine
oxygenation, gave a much more complex mixture of compounds on decomposition. Thus, although reaction with
sodium methoxide afforded caprolactam (low yields) and
benzophenones, varying amounts of benzanilides, cyclohexanone, benzonitriles, and diarylmethanols were also
Pyrolysis of cyclic peroxyamines derived from acyclic
ketones caused a fundamentally related decomposition to
give ketones, amides, nitriles, and acids; the nitriles and
acids were derived from imides, in turn produced from
the diradicals by loss of alkyl radicals[']].
but when the enamine also had a carbonyl group suitably
positioned, intramolecular cyclization of the intermediate
r-hydroperoxyamine led to a cyclic peroxide where the
nitrogen was not part of the
CONH,
i93)
v
H3C-CN
J
+ HSCZ-CN + H~CZ-COZH
+ H3C-C0,H
The dioxazolidines derived from aldehydes have a secondary-tertiary or disecondary peroxide system, and, in consequence, are easily decomposed by bases ( e .y. triethylamine),
by a normal Kornblum-De La Mare mechanism, to yield
a carbonyl compound and amide.
Surprisingly, although 3,3-pentamethylene-5-methyl-1,2,4dioxazolidine (92) similarly gives cyclohexanone and acet192
(94)
The product of reaction of cyclohexanone with urea, earlier
reported to have the structure ( 9 3 ) and to give the cyclic
] , thought to be
peroxide ( 9 4 ) on a u t ~ x i d a t i o n [ ~is~ now
(95) leading to a hydroperoxide (Y6)[541.
Received: November 2X. 1972 14 954 I F ]
German version : Angew. Chem. 85. 850 ( I 973)
___~_
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Sesquiterpenes
By Gerhard Rucker[*]
Of the 4000 or so terpenoid natural products known today, whose carbon skeleton can
bedivided up into isopentane units by the"isoprene rule" (Clo,rnonoterpenes; Cis, sesquiterpenes; C,,, diterpenes; C, 5 r sesterterpenes;C,,, triterpenes; steroids; carotenoids; polyprenes),
the sesquiterpenes, numbering about 1000, represent the largest single class. According
to the well founded concepts developed in recent years for the biogenesis of their highly
diverse carbon skeletons, the present report is divided into nine sections dealing respectively
with farnesanes, bicyclofarnesols (drimanes, iresanes), bisabolanes, cadinanes, humulanes
and caryophyllanes, germacranes, "hydroazulenes", selinanes and eremophilanes, and maalianes and aristolanes. Further groups of sesquiterpenes can be derived from each of these
structural types.
1. Introduction
The chemistry of the sesquiterpenes with their 15 carbon
atoms~~correspondingto three isopentane units[*] Prof. Dr. G. Rucker
lnstitut fur Pharmazcutische Chcmie d e r Universitiit
44 Miinster, Hittorfstrasse 58 ( G e r m a n y )
arranged in an acyclic or mono-, bi-, tri-, or tetracyclic
skeleton has undergone a period of rapid development
during the past two decades following the introduction
of chromatographic separation techniques and physical
methods of structural analysis. In 1953 about 16 sesquiterpene skeletons were known corresponding to about 30
compounds, in 1964 the respective figures were 40 and
793
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