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More about - and -Succinimidyl Radicals Ring Opening Reactions.

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59, 8712f (1963).
[120] 0. S. Orroshchenko, M. Goshaev, A. S . Sadykoc, N. V. Kuznetsova,
USSR-Pat. 253066 (1969); Chem. Abstr. 72,121 372t (1970).
[I211 R. F. Homer, 7: E. Tomlinson, J. Chem. SOC.1960, 2498.
[I221 E. Hardegger, E. Nikles, Helv. Chim. Acta 40, 2421 (1957).
[I231 G. L. Cook, F. M . Church, J. Phys. Chem. 61, 458 (1957).
[124] F. Kuffner, F. Straberger, Monatsh. Chem. 88, 793 (1957).
[125] R. F. Homer, J. Chem. SOC.1958, 1574.
[I261 A. M. Jones, C . A. Russell, J. Chem. SOC.C1969, 2246.
[I271 G. Bianchetri, Farmaco (Pavia) Ed. Sci. 11, 346 (1956); Chem. Abstr.
53, 9209f (1959).
1943,404.
[I291 I. Suzuki, Pharm. Bull. 4, 211 (1956).
[130] R. A. Abramouitch: Heterocyclic Compounds. Vol. 14: Pyridine and
its Derivatives. Wiley, New York 1974. Part 3, Chap. 9, p. 41.
[I311 P. Hong, H. Yamazaki, Tetrahedron Lett. 1977, 1333.
[I321 K . P. C. Vollhardt, A . Naimann, Angew. Chem. 89, 758 (1977); Angew.
Chem. Int. Ed. Engl. 16, 708 (1977).
[133] H . Yamazaki, N. Hagihara, J. Organomet. Chem. 21, 431 (1970).
[134] H . Bonnemann, W Brijoux, unpublished work (1975).
[I351 R. A. Abramouitch: Heterocyclic Compounds. Vol. 14: Pyridine and
its Derivatives. Wiley, New York 1975. Part 4, Chap. 15, p. 189.
C 0 M M U N I CAT10N S
recognized['], the o type undergoes this cleavage reaction
while the K type does not.
More about n- and o-Succinimidyl Radicals: Ring
Opening R e a c t i o n s [ * * ]
By Philip S. Skell, James C . Day, and Joseph P . Slangs"]
Until recentlyf1- 31 the reactions of the succinimidyl radical
were virtually unknown, or unrecognized, with the exception
of its intermediacy in the rearrangement of N-bromosuccinimide (NBS) to P-bromopropionyl isocyanate (I ), a reaction
which had defied ~nderstanding'~].
O
n
0 -.+
0
II
Br<H2CH2C-N=C=0
I)r
6,
(1)
NBS
The various parts of the puzzle are now accommodated
by the hypothesis that succinimidyl radical undergoes rapid
and reversible ring cleavage, and that trapping of the openchain form leads to the P-halopropionyl isocyanate. Of the
two types of succinimidyl radicals which have been
-~
[*I Prof. Dr. P. S . Skell, Dr. J. C. Day, J. P. Slanga
Department of Chemistry, The Pennsylvania State University
University Park, Pennsylvania 16802 (USA)
[**I This work was supported by the Air Force Office of Scientific Research
(2748C).
Angew. Chem. Int. Ed. Engl. 17 (1978) No. 7
The assemblage of experimental results which are to be
accommodated by this hypothesis are summarized below.
1) Irradiation (or heating, with benzoyl peroxide initiation)
in the presence of alkenes results in 25-90% yields of acyl
isocyanate (I ) for N-bromo- (NBS) and N-iodosuccinimide
(NIS); no isocyanate is formed if N-chlorosuccinimide (NCS)
is used, or any of the N-halophthalimides or N-haloglutarimides, despite the fact that the same H-abstractions, additions
to alkenes, and additions to arenes are observed as for NBS
and NIS.
2) Within large limits the above results are insensitive to
changes in olefin concentrations (see also [4b]).
3) In the presence of large concentrations of alkenes (or
benzene) no isocyanates are obtained; the succinimidyl moieties are found as succinimide (H-abstraction) and in 1,2adducts to the olefin (or benzene)[3!
4) In the presence of Br2 or Iz no isocyanates are formed;
only H-abstractions occur, among them abstractions which
cannot be attributed to Br' or 1'.
5) One or more alkyl substituents on NBS have only a
small effect on its reactivity in the presence of alkenes, as
determined in competition reactions in which the rate of disappearance of the NBS derivatives is monitored[5'. However,
the product is 100 % isocyanate when the alkyl-substituted
NBS is used, whereas under the same circumstances NBS
itself gives 25-60 % yields of isocyanate (and succinimide
arising by H-abstraction). In the presence of alkenes the succinimidyl radicals are exclusively 0 type.
6) On the other hand, in the reaction of N-bromo-3,3dimethylsuccinimide with neopentane in CHZCl2in the presence of Brz, no isocyanate formation is observed (absence
of 2230cm- band). The reaction products are neopentyl
bromide, BrCHCl', and 3,3-dimethylsuccinimide. In the presence of Br2 the succinimidyl intermediate is exclusively of
7c type. There seems to be no significant interconversion of
o and 7c types under these reaction conditions.
515
7) The percentage of NBS converted into isocyanate decreases with decreasing concentration of NBS, without affecting the relative rates of the competing processes.
In the presence of halogens the succinimidyl generation
step (X*+ NXS) is almost thermoneutral and thus can produce
only the ground state, n radicalI2I, which does not correlate[61
with the ground state of the open-chain radical. On addition
of alkene but no halogen, the alkene functions as a halogen
scavenger and thus makes possible the generation (R' NXS)
of the o radicalI2I, which does correlateL6]with the ground
state of the open-chain radical. Thus, in the presence of
halogen, n-succinimidyl radicals arise which can abstract hydrogen but do not form isocyanates; in the presence of alkenes,
0 radicals are produced, leading to competition between ring
opening and hydrogen abstraction.
o-Succinimidyl is postulated to undergo a rapid, reversible
ring-opening reaction; thus it is possible to explain all the
observations.
+
b-H,
These new results add force to the earlier suggestion that
thermal chain reactions involving succinimidyl radicals can
involve either K or o states of the radical.
Received: March 29, 1978 [Z 974 IE]
German version: Angew. Chem. 90, 546 11978)
CAS Registry numbers:
(I), 18926-24-4; NBS, 128-08-5; cis-3,4-dideuteriosuccinimide, 66633-57-6
[ I ] J . G . Traynham, Y S. Lee, J. Am. Chem. SOC. 96, 3590 (1974); J . C.
Day. M . J . Lindstrom, P . S. Skell, ibid. 96, 5616 (1974); P. S. Skell,
J . C . Day, ibid., in press; Acc. Chem. Res., in press; imidyl radicals
are H-abstractors of low discrimination; they add readily to alkenes
and arenes.
[2] P . S. Skell, J . C . Day, J. Am. Chem. Soc. 100 (1978), in press.
[3] J . C. Day, M . G . Kotsaros, W D. Korher, A. E . Srorr, P . S. Skell,
J. Am. Chem. SOC.100 (1978), in press.
[4] a) H . W Johnson, Jr., D . E . Bublirz, J . Am. Chem. SOC.79, 753 (1957);
b) 80, 3150 (1958); c) J . C. Martin, P . D. Bartlerr, ibid. 79, 2538 (1957).
[5] J . C. Martin, personal communication; we confirm those results.
[6] 7: Koenig, R. A. Wielesek, Tetrahedron Lett. 1975, 2007.
[7] Analogous reactions of maleic anhydride have been reported: C. R.
Childs, Jr., K . Bloch, J. Org. Chem. 26, 1630 (1961).
[S] The 3,4-dideuteriosuccinimides were analyzed by mass spectra (parent
ion, m / e = l O l ) and IR. The intensity of the C H D bands at 700 and
5lOcm-' decreases by 7 0 % on reaction of [D2]-NCS in the presence
of alkenes while new bands appear a t 730 and 525cm-'.
Alkene, Arene
I.
Methylenesulfur Tetrafluoride H2C=SF4[**]
Reactions of the o-succinimidyl radical in H-abstraction
and additions to alkenes or arenes are very fast, the rates
being almost encounter-controlled[31.
NBS and NIS can trap
the open-chain radical, the much less reactive NCS cannot;
thus there is no ring-opened product from NCS. The rate
constant k must exceed 108s-'.
With one or more alkyl substituents on the ring, open
chain secondary and tertiary radicals can arise, which are
more stable than the cyclic radical. Therefore, formation of
open-chain radical is rapid ; isocyanates are produced exclusively. The ring-opening rates k probably approach 10"s- ',
since H-abstractions by the o-succinimidyl forms are not
observed. O n the other hand, in the presence of Br2, the
N-bromo-3,3-dimethylsuccinimideyields a K-succinimidyl
which cannot undergo ring opening, and thus only H-abstractions are observed.
A critical test of this rationalization was obtained by demonstrating that in the NCS reactions (presence of alkene) in
which succinimide is the only product (no isocyanate is
observed), some of succinimidyl radicals must spend some
time in the open chain form before they abstract a hydrogen
atom to form succinimide.
cis-3,4-Dideuteriosuccinimide was synthesized by reaction
of maleimide with D 2 over a palladium catalyst[']; this was
converted into [D2]-NCS and [D2]-NBS. Reaction of the
[D2]-NBS with neopentane in the presence of Br2 (CH2C12
solvent) resulted in formation of pure cis compound, identical
(IR) with starting material. These are conditions for intermediacy of the x-succinimidyl[21. On the other hand, reaction
of [D2]-NCS in the presence of alkene produced analytically
pure dideuteriosuccinimide[*], which is 70 % cis and 30 %
trans (IR). These are conditions for the intermediacy of o-succinimidyl[21,and the experiment demonstrates the intermediacy of an open-chain species in the conversion of NCS
into succinimide, an open-chain intermediate which is not
trapped by NCS to produce an isocyanate, but instead, closes
the ring and then abstracts hydrogen.
516
By Gert Kleemann and Konrad Seppelt[*l
We have now synthesized the carbon analog of H W S F 5 [ 1 1
and H2N-SF,[21, namely H3C-SF5, in the following
manner: Sulfur chloride pentafluoride reacts in the usual wayc3]
with ketene to give SF5CH2-COCl, which by hydrolysis
is converted into the acid SF5CH2-COOH. Hunsdiecker
degradation of the silver salt of this acid yields SF5-CH2Br,
which in turn is reduced to the desired compound H3C-SF5.
SF4 + Clz
+ CSF
250°C
CFCI,, 20°C
SF,Cl+ CHz=G=O
SF5-CHz-COCI
SFsCl+ CSCI
SF5-CH2-COCI
B.p. 4S°C/130 mbar
A
SF5-CH2-COOH
- HCI
Subl. 40°C/0.5 mbar, M. p. 64°C
SFs-CH2-COO-Agf
SF5-CHzBr
Zn/HCI
CFCI
+ Br2 -4
COz + AgBr + SF,-CH2Br
B. p. 75°C
H3C-SF5
B.P. 26"C, M.P.-11.5"C
Methylsulfur pentafluoride, which is colorless and stable towards hydrolysis, was characterized like all the precursors
by elemental analysis and on the basis of mass, IR, and NMR
spectral data. The 19F-NMR spectrum of H3C-SF5 shows
a typical AB4 pattern, the B4 resonances appear as a quartet
( J H=~9.8 Hz), and the H-NMR signal of the methyl group
(6H=3.4) is split into a quintet.
[*] Priv.-Doz. Dr. K. Seppelt, Dipl.-Chem. G. Kleemann
Anorganisch-chemisches Institut der Universitat
Im Neuenheimer Feld 270, D-6900 Heidelberg 1 (Germany)
This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
[**I
Angew. Chem. I n t . Ed. Engl. 17 (1978) No. 7
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