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HexamethyldisilaneIodine Convenient In Situ Generation of Iodotrimethylsilane.

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of (6c) [>90%, m.p. 127°C (methanol/CCI,); ( 7 4 : m.p.
145°C (CCI,/CHCI,); J i , l %, l , J 2 . 4 ~ 4 ,J 4 . 5 I~, J i (,=4.5,
J(,.7= 8, J7.x
= 7, J,, = 4.5 Hz]. During the long time required
for elimination of HC1 (24 h) the product uniformity is lost:
for example, after complete reaction with KOH/methanol
(20 "C, 24 h) only 30-35% of (#a) is obtained [m.p. 207 "C
(subl.); (86); m.p. 197°C (subl.); 'H-NMR (CDCI,. 360
MHz): 6=5.65 (t. 8-H), 3.44 (m, 2-, 4-H), 3.34 (m. 1-. 5-. 7-,
9-H), 2.21 (s, OCH,); J7.8 (J,..))= 1 Hz; "C-NMR (CDCII):
6 = 170.3 (CO), 67.0 (C-8), 58.7 (C-7. -9), 52.3 (C-1, -5). 48.2
(C-2, -41, 20.9 (CH,)]; products resulting from substitution at
C-2, C-4 and transannular ether formation arise preferentially["'. The yield rises to the fairly respectable value of 4550% of (#a) [42-48% based on (46)l-with similar by-products-on use of the reagent sodium glycolate/THF which
has proved of value in similar cases1']: only nonspecific decomposition occurs with DBN.
The critical step en route from (5b) to ( l l a ) is epoxidation:
the diacetate (5b) is resistant to m-chloroperbenzoic acid (in
C2H4Cl2) between 25 and 80°C. The diol (50) is also oxidized very slowly (3 d. 20°C) yet with an expectedly high
trans-selectivity; polymeric material is accompanied by 45%
of (1Oa) [m. p. 175 "C (ethyl acetate/benzene); (lob): m. p.
119- 120 'C (CCI,); J 2 . 4 = 4, JI.5 = 7, J,,, = 4.5. J(,.7 = 9, J7.s = 8
Hz] and traces of (7u) [m. p. 115 " C (ethyl acetate/benzene);
1, J,.,=8,
J7,=6.5, J,,,=4.5 Hz]. Nor
JI,2=1.5,J 2 . 4 = 4 rJ 4 . 5
could the early initiation of decomposition and secondary
reactions be delayed by variation of the reaction conditions
(peracid, temperature, buffer). No (fOa) is formed with
CF,C03H/Na2HP04 (CHLCL,20 "C). Epoxide ring closure
(IOa)+(lla) is fast and practically uniform [85-90'%; 3640% based on (Sb), m.p. 93-94°C (acetone/CCI,); ( I l b ) :
m.p. 85 "C (CCI4/pentane); 'H-NMR (CDCl,, 360 MHz):
6=4.90 (d. 8-H). 3.59 (dd, 1-H), 3.35-3.45 (m. 4-, 5-H). 3.30
(d, 9-H), 3.20 (dt, 2-H), 3.16 (dt. 7-H), 2.21 (s, OCH,);
Ji,z=3, J,,,=4.5. J2,4=3, J4,5=0, J 5 . 7 ~ 5 .J,.,=5.5, J , , = O
Hz: "C-NMR (CDCI3): 6= 170.4 (CO), 73.2 (C-8). 57.5, 55.8
(C-7, -9), 51.9, 50.8, 49.2, 48.6 (C-1, -2, -4, -5)].
The alternative of first converting (5a) into (%-the conformation having quasi-trans-diaxial OH/Br substituents is
readily accessible-and epoxidizing the product is less favorable. Although (Ya) is formed quantitatively under standard
conditions [m. p. 93-94 " C (ethyl acetate/benzene); (Yh):
m. p. 108-109 "C (CCI,)], its epoxidation is even slower and
more complex than that of (5a) and, moreover, non-stereoselective [ca. 5-10% of each (#a) and (lla)]lsl.
Compounds (5)-(14) are fully characterized by elemental
analysis and spectral data (MS, IR, 'H- and "C-NMR), and
the stereochemistry of the end products (8) and (11) is chemically confirmed, e. g. by oxidation to the tropone trioxides
and by comparison with the exo/endo a1cohols"l formed
from the latter compounds.
Received. June 21. 1978 [Z 39 IE]
German ~ e r s i o n Angew.
Chem. 91, 646 (1979)
Publication delayed at author\' request
CAS Registry numbers:
(4h). 59Y92-03-9: (JuJ. 67598-52-1: (5hJ. 67598-53-2: ( 6 ~ ) 67598-54-1.
h 7 s ~ n - s 7 - 6 :(7u). 67598-5x-7: ( 7 ~ ) 6
. 7s~~-598 , (7d). 67598-60-1: (Xu), 67598-61-2: IXh). 67598-62-3: IOuJ. 67598-63-4: ( Y h j .
67598-64-5; ( / O n ) . 67650-77-5: //ObJ, 6759X-65.6. ( 1 / u ) . 67650-78-6: ( 1 l h J .
[I] a) H. Prmzhach. R. Srhwe>inger. M Breunrn,yer. R. Gullenhump. D. HunkIer.
Angew. Chem. 87. 349 (1975); Angew. Cheni. Int. Ed. Engl 14. 347 lIY75),
and references cited therein; b) cf.. c s.. the synthesis of atreplamine fro111 ci\bensene trioxidc. R. Schnw~ingcr.H. Prmihuch. rhid 87. 625 (19751 and 14.
630 (tY75). respectively.
0 Veriag
Chemie, GmbH, 6940 Weinherm. 1 Y 7 Y
[2] The third isomeric alcohol ( & < t )
/12) has been o b t a n e d Irrtni ~ [ 3 . ~ t i w
pone triohide: tI Pr;n:bui/i. W. Scppcli. / I Frrr:. t o he p u h l i ~ l i c ~ l
131 Attenipted radical halogenation o f the CHI group i n ~i.s-tropilidrnrtrioride
141 led only to suhstitution in the epaxide ring.;: ('h. R u d w . Di\\srtati(in.
Universitat Freiburg 1979.
[4] H. Prin:bo</i, ( I . Rucker. Angew. Chem. W. 61 I ( I Y 7 6 ) ~A n g e w Chem Int.
Ed Cngl. 15. 5.59 ( lY76).
IS] W. T o d i i t ~ r m a nFortschr.
Chem. tvrsch 1.7. 37X (1970).
[h] I.ther\ and chloride\ 0 1 type f1.i) and 114). X=OCH,. CI. could he irolatt.d
and characteriLed.
171 R. Schwe$mgcv, H. Prin:buch. Angew. Chem 84. 9YO (lY7?): 4 n g e w Chem.
Int. t d Engl / / . 942 (lY72).
[XI The hitherto unknown ris-2.3:4.5-tropone dioxide ( m p. XX C. 44-60"L:
J~,,=12. J i . = 3 5 . J , , = 4 H 7 ) c a n heuhtainedi'ra
/ciu), e.,q hy oxidation with RuOd ( R u 0 2 . 2 equiv NalO,. CHCI,/H:O.
20 C )
Hexamethyldisilane/Iodine: Convenient In Situ Generation of Iodotrimethylsilane['*]
By George A. Uiah, Suhhash C. Narang, B. G. Balurum Gupta, and Ripudaman Ma1hotra"l
lodotrimethylsilanel" has recently found extensive use in
organic syntheses. Because of the relative difficulty of preparation and its hydrolytic and photoinstability, emphasis was
placed on continued work on the in situ generation of the
reagent. Work in this area has resulted in the use of phenyltrimethylsilane/iodine"',
allyltrimethylsilane/iodine, and
These reagents, however, can either produce undesirable byproducts or involve tedious syntheses of starting materials.
Recently, chlorotrimethylsilane/sodium iodide was also introduced as an iodotrimethylsilane equivalent, but its utility
is confined to the essential use of acetonitrile as solvent[41.
We now wish to report the use of hexamethyldisilane/iodine [(2)/12] as an extremely effective and mild in situ iodotrimethylsilane reagent giving no by-products. This reagent can
be advantageously used for the mild cleavage of esters (/),
carbamates (5). ethers (3), and sulfoxides. Alcohols can be
equally well transformed into corresponding alkyl iodides
with the reagent.
Esters ( I ) are cleaved to the corresponding acids in very
high yield. The reaction was applied with equal ease to methyl, ethyl, and benzyl esters of aliphatic and aromatic carboxylic acids.
I Me.SiSiMe* /2)/12
2 H,O
+ R'I
Aliphatic ethers (3) can be cleaved to the corresponding
alcohols or further transformed into alkyl iodides by varying
the reaction conditions. When cyclohexyl methyl ether (3d)
was reacted with HMDS/12 reagent in chloroform solution at
[ * ] Prof. Dr. G . A. Olah, S . C . Narang, B. G. B. Gupta. R. Malhotra
Hydrocarbon Research Institute. Department ot Chemistry
University of Southern Calitbrnia
University Park. Los Angeles. Calilbmia YO007 ( U S A )
[**IPart 74 i n the Series Synthetic Methods and Keactions. Support lor this
work hy the National Science Foundation and the National Institute\ 01 Health
is gratelull? acknowledged. Part 73 ( L A Oluh. 'l D. VmAnr. M Art.unwhi.
Tetrahedron Lett, in press.
i)S70-0833/ 79/0808-0612 $ 02.S0/0
Angeu. Chem. Inl. Ed. Lngl 1 8 f / Y i Y / No. N
room temperature, cyclohexanol was obtained in excellent
yield. When the reaction mixture was heated under reflux in
the absence of chloroform, cyclohexyl iodide was obtained
with no alcohol present. Alcohols themselves can be cleanly
converted into the corresponding iodides.
General Procedure
To a solution of hexamethyldisilane (2)I"l and I z (for
amounts, see Table 1 ) in chloroform (15 ml). the substrate
[ester (1), ether (3), or carbamate (5)] ( 5 mmol) is added with
continuous stirring under a nitrogen atmosphere. The reaction mixture was then heated under reflux and the reaction
monitored by TLC and 'H-NMR [cf. ref. ''I]. Usual workup
afforded the desired products, which were purified by crystallization or distillation.
A similar procedure was employed in the conversion of alcohols (4) into iodides and in the deoxygenation of sulfoxides to sulfides.
I t was observed that cleavage of both esters (1) and ethers
(3) is catalyzed by excess iodine in the system (see Table
Received: May Y. I974 [ Z 252a It;]
German version: Angew. Cheni. 0 1 . 64X (1979)
1 p .
Table I Reactions ofesters (/). ethers (-3). alcohols 14). and carhamate, (5) with hexamethyldisilane (?)/I:.
agreement w i t h those of authentic samples.
Substrate: ( 2 ) .l 2
(molar ratio)
I -Adamantdnecarboxylic acid
Cinnamic acid
Phenylacecic acid
I :0.55:0.55
Methyl I-adamantanecarhoxylate
I :
1.0.9: 1.05
I .0.55:0.55
I :
I :
I :0.55:0.55
I :0.55 -0.55
1 :0.55 .0.5s
Bensyl methyl ether
Cyclohexyl methyl ether
1 -Oh6:0.66
Ckclohcxyl ethyl ether
Benmic ~ c i d
Ben7yl iodide
B e n ~ i 'icid
B c n i v l henmate
Methyl cinnamate
t t h y l phenyldcetate
I :O.66,0.66
I: O f : 0.7
l.thyl hensoate
T h e IR. N M R and m.p. or b.p o l t h r isolated product, werc
Bensyl iodide
Cyclohexyl iodide
Cyclohexyl iodide
I -Nunand
I -Adamaiitanol
B r n i y l alcohol
V-Phenyl methylcarbamate
Cyclohexyl iodide
Nonanyl iodide
Adamantyl iodide
Bensyl iodide
Beniyl iodide
0. I
f ~ r rB- uty l
r w - B u t y l iodide
Bnc-GI y-OByI
I:I.l:I 1
I : l . I :1 . 1
Benzyl iodide
100 [h]
100 [b]
100 [b]
100 [h]
100 [h]
100 [ h ]
100 [h]
[a] Isolated yield of' the product. [bl Product composition determined by NMR spectroscopy
The present reagent was also found to be more selective in
of protective groups frequently employed in
peptide chemistry' For
carbarnates (5) can be
cleaved cleanly in the presence of a benzyl ester.
R N H C O 1R '
5 min
CAS Registry numbers:
(1U). 93-89-0; ( l h ) . 120-51-4: (IC). 71 1-01-3: (Id). 103-26-4: / / P ) . IoI-97-3: (2).
1450-14-2: (.?uJ,100-66-3. (36). 103-73-1; (.k),53X-Xh-3: f3d). 931-56-6: (.?<,), 93292-3: ( 4 ~ )108-93-0:
(4h). 143-OX-X: ( 4 0 . 76X-45.6. (4d). 100-51-6: (Cu). 2h03-103: 1.56). 17 136-36-6: 1 . 5 ~ ) . 4530-20-5. /W). 54244-69-X: hensoic acid. 65-X5-0: henzyl iodide, 620-05-3; I-adamantanecarhoxylic acid. 828-51-3: cinnamic acid. 621X2-9: phenylacetic acid. 103-X2-2. phenol. IUX-Y5-2. cyclohexand. IOX-Y3-0: cyclohexyl iodide. 626-62-0: nonyl iodide. 42x2-42-2: I-adamantyl iodide. 76X-Y34: aniline. 62-53-3: glycine. 5(1-40-6: r ~ . r r ~ h u iiodine.
30 min
Sulfoxides, including dibenzyl sulfoxide, diphenyl sulfoxide. dibutyl sulfoxide, and tetramethylene sulfoxide are also
rapidly deoxygenated by (2)/12 to the corresponding sulfides
in quantitative yield.
An,qrU C'heni. Inr. Ed. E q l . 18 fIY7Oi N o . X
T. L / j u . G. A . O h h . Angew. Chem. 88. X47 (1976): Angew. Chem. Int. Ld
t n g l 1.5. 774 (1976): G. A Oluh. H . G. B Gupru, S. (I Nurun,y. Synthews
1977. 5x3. M. E. Jun,q. M. A l-),srer. J . Chem. Soc. Chem. C o m m u n . 1 Y 7 X
315. and relerences cited therein.
[2] 7 I.. Ho. G. A. Oluh. Synthesis 11/77. 417.
0 Verlug Chemie, GmbH. 6940 Weinhelm, I 9 7 9
$ 02..70/0
I31 M. E. Jitng. 7 A . Bliiinoihopf: Tetrahedron Lett 1'17A'. 3057.
141 G A . Oluh, S. C. Xurung, B G. B Giipru. R Mulhorm. J . Org. Chem. 44, 1247
[Sj BenAewr rr a/ have ohrerved \imiIar catiilysi\. R. / I . BmAewr. perhonal communication.
[h] ( 2 ). which i \ commercially available lroni PCK Rehearch Chemicals. Inc
can be readily prepared from chlorotrimeth~l~ildne
and lithium: \ee H Sokiimi, A . Okada, J . Organomet. Chem. 36, C 13 (1972): D.A Sefrz. L. Ferrefra.
Synth Ctimmun. I). 451 (197Y).
Formic Anhydride[**]
By George A . Olah, Yashwant D. Vankar, Massoud Arcanaghi, and Jean Somrner["
Formic anhydride ( I ) , the parent carboxylic acid anhydride, has long eluded preparation and characterization.
Olah et al.['' first reported in 1955 the possible formation of
(1) in the reaction of formyl fluoride with metal formates at
low temperature. No spectroscopic observations or physical
data were, however, obtained. In 1964, Muramatsu et a/."' assumed the intermediacy of (1) in the formylation of p-nitrophenol and L-leucine with an ethereal solution of formic acid
and dicyclohexylcarbodiimide (DCC); no isolation was attempted nor were physical data obtained. Stevens et al."', in
the same year, reported the formation of (I) by the thermal
disproportionation of formic-acetic anhydride and of mixtures of formic acid and carboxylic anhydrides: proof of formation of (1) was based on the appearance of a 'H-NMR
singlet at 6=9.0, which, however, might have been due to a
mixed anhydride or other species.
We now wish to report the unequivocal preparation of formic anhydride by four independent methods (A-D) and its
characterization by 'H-NMR. "C-NMR, and IR spectroscopy. Further, the ethereal solution of (1) (obtained by any of
the four methods), gave p-nitrophenyl formate in uniformly
good yield when allowed to react with p-nitrophenol.
In the formylation method (method A ) , formyl fluoride
dissolved in anhydrous ether is reacted at - 78 " C with an
excess of sodium formate in the presence of formic acid. In
the three dehydration methods (methods B-D), formic acid
(2 mol. equiv.) was dissolved in anhydrous ether at - 78 "C
and treated with a base (2 mol. equiv.; no base required in
case B ) followed by one mol. equiv. of the dehydrating reagent.
Prof. Dr. G. A. Olah. Dr. Y. D. Vankar. M. Arvanaghi
Hydrocarbon Research Institute. Department of Chemistry
University of Southern California
University Park, Los Angeles. California 90007 ( U S A )
Prof Jean Sommer
Institute de Chimie. Universite Louis Pasteur, Strashourg (France)
0 Verlag C'hemre. GmbH. 6940 Wernheirn, 197Y
Received: June 7. 1979 [Z 2S2h IE]
German version: Angew Cheni. V i . 649 (1979)
CAS Kegktry numbers
/ I / , 15SX-67-4: formyl tluoride. 1493-02-3: ic~rnmica c ~ d 64-IX-0
[I] G A . Olrih. A . fuI./urh. S. Kuhii. G. Vunonsi in: Elektronentheorie der homoopolaren Bindung. Akademie Verlag. Berlin 1951, pp. 79- 94: G. A. Oluh.
S. J. Kuhn in G. A. Oluh: Friedel-Craits and Related Reactiona Wiky-Interscience. New York 1964. Vol. 111. Part 11. p. 1154.
[ 2 ] I. Muramurm. M . Iror. M l w p , A . Hugiruni. Bull. Chem. Soc. J p n . 17. 756
131 W S r e t e n ~A . Vuri E.T. Rec Trav. Chini. Pays-Ba\ X.i. Xh3 (1964). K. .Schi//.
J. W. Scheeren. A. Vun Er. W. Siei~enl:ihid. S4. 594 (1965).
[2 +2]-Cycloaddition of a Vinyl Cation'**'
By Giinter Nammen and Michael Hanack"'
The reaction of propargyl halides and cyclopentadiene in
pentane with silver trifluoroacetate has recently been reported[''. The allenyl cations formed in the reaction undergo
I ,4-addition to cyclopentadiene and, after hydrolysis of the
trifluoroacetate. afford cyclopentenols: [4+ 31-cycloaddition
leads via vinyl cations to bicyclic products.
We report here on the first cycloaddition with a vinyl cation"', which was generated from a vinyl halide by solvolysis
in the presence of silver salts. The vinyl halide chosen was 1bromo-l-(4-methoxyphenyl)-2-methyl-l-propene(1). whose
ready solvolysis to the vinyl cation (2) is welI-knownl7l.
Reaction of (1) in cyclohexene with silver trifluoroacetate
and pyridine as buffer at room temperature leads almost
quantitatively to the vinyl ester (3a). The products (5) and/or
its isomer (8) expected to be formed on reaction of (2) with
cyclohexene were obtained in only 1% yield.
On the other hand, when a solution of ( I ) in cyclohexene
is allowed to react with silver tetrafluoroborate and pyridine
(molar ratio 1.0: 1.6:2.0) at 25 "C, subsequent workup with
aqueous ammonia affords a mixture of 82% 8-(4-methoxyphenyl)-7,7-dimethylbicycl0[4.2.0]octa-l(8)-ene (S), 11% 1fluoro-l-(4-methoxyphenyl)-2-methyl-1-propene
7% 1-(2-fluorocyclohexyl)- 1-(4-methoxyphenyl)-2-methyl-1propene (7) in 70-8096 yield. The structure of the products
was confirmed by 'H-, "C-NMR, and mass spectroscopy
(Table 1). At 150°C (5)isomerizes smoothly within 3 h to 1( 1-cyclohexenyl)- 1-(4-methoxyphenyl)-2-methyl-1-propene
Support d o u r work by the National Institutes oS Health and the National
Science Foundation is gratefully acknowledged. as is a Senior U S. Scienti\t
Award of the Alexander von Humholdt lbundatton to G. A . 0 . facilitating this
The 'H-NMR spectrum (-40°C) of (1) formed by all
these methods showed a singlet at f i = 8.45 (TMS as external
standard). The proton decoupled "C-NMR spectrum
(-40°C) of the same solution showed a singlet at 6 = 158.54,
which on coupling displayed a doublet with Jt2CH= 242.8 Hz.
The corresponding signals in the spectra of formic acid lie at
S=8.83 and 163.38 (JllcH=216.3 Hz); thus the C and H
atoms are, as expected, more strongly shielded in the anhydride (1) than i n the acid. The infrared spectrum of ( I ) , recorded at -78°C using a Beckman Instruments low temperature IR cell, shows strong carbonyl stretching frequencies at 1795 c m ~' and 1775 cm ~ 'characteristic
of an acid
Attempts to isolate (I) from the ethereal solutions by distillation, including low temperature distillation, gave only
products contaminated with formic acid.
DiplLChem. G. Hammen. Prof. Dr. M. Hanack
lnstitut fur Organische Chemie der Universitat
Lehrstuhl fur Organische Chemie I 1
Auf der Morgenstelle I X . D-7400 Tubingen (Germany)
I**]This work
p a s supported by the Deutsche Forschungsgemeinschaft
0 5 7 0 - 0 X 3 ~ / 7 Y / 0 X 0 H - 0 6 / 4$ 02.51/11
AnKen, Chem. I n / . Ed Engl. 1 8 0 9 7 0 ) No. 8
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iodotrimethylsilane, generation, hexamethyldisilaneiodine, convenient, situ
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