J . Org. Chem. 1987, 52, 1844-1847
1844
Rearrangement of (Substituted benzy1)trimethylammonium Ylides in a Nonbasic Medium: The Improved Sommelet-Hauser Rearrangement Mitsuji Nakano and Yoshiro Sato* Faculty of Pharmaceutical Sciences, Nagoya City University, Tanabe-dori, Mizuho-ku, Nagoya 467, Japan
Received August 6, 1986
Benzyl quaternary ammonium ylide formation in a nonbasic medium was accomplished by fluoride anion induced desilylation of benzyldimethyl[(trimethylsilyl)methyl]ammoniumbromide (3a) and ortho- or para-substituted benzyl analogues 3b-k. Treatment of 3 with CsF in HMPA at room temperature gives high yields of the Sommelet-Hauser rearrangement products 7 from 3a and methyl-, acetoxy- and chloro-substituted analogues 3b-f. However, formation of the Stevens rearrangement products 8 is competitive for the reaction of compounds 3g-k having strong electron-withdrawingsubstituents such as acetyl, cyano, and nitro groups. From the ocyano-substitutedanalogue 3h,a considerable amount of para Sommelet-Hauser rearrangement product is isolated. The two base-promoted isomerizations of benzyl quaternary ammonium salts are well-known as the Stevens rearrangement and the Sommelet-Hauser rearrangement.' When structurally feasible, both rearrangements may occur simultaneously, thus limiting their synthetic utility, and their ratio is affected by the kinds of bases and solvents employed.2 The only such reaction reported to give almost exclusively the Sommelet-Hauser rearrangement product involves treating benzyltrimethylammonium halides with sodium amide in liquid ammonia, and it provides a convenient synthetic route to N,N-dimethy1-2-methylben~ylamine.~However, this rearrangement does not occur if a substituent on the benzene ring prevents the formation of the required ylide intermediate. For example, halogen substituents decrease markedly the yield of rearrangement product, apparently because of benzyne f ~ r m a t i o n . Attempts ~ to rearrange (p-cyanobenzy1)ammonium salts under these conditions have fai1ed.j It has been reported that the reaction of benzyldimethyl[(triorganosilyl)methyl]ammonium halides with lithium aluminum hydride or sodium amide involves cleavage of the carbon-silicon bonds to give ammonium ylide intermediates.'j Vedejs et al. reported that [ (trimethylsilyl)methyl]ammonium salts can be desilylated with fluoride anion and that the resulting intermediate undergo reactions characteristic of nitrogen ylide.' Accordingly, we have investigated the use of fluoride anion to cleave the Si-C bonds of benzyldimethyl[(trimethylsilyl)methyl]a"onium halides 3 in search of a new route to the Sommelet-Hauser rearrangement. in a nonbasic medium. Benzyldimethyl[ (trimethylsilyl)methyl]ammonium halides 3a and 3a' and ortho- and para-substituted analogues 3b-f,h,i were prepared by reaction of the corresponding benzyl halide derivatives 1 with [(dimethyl-
Scheme I
Scheme I1
3
F-
A
-Me3SiF
[
R1 R2-@CH2fCHi
1
6
a
7 R1 = CN R2 = H
9
Table I. (Substituted benzy1)dimethyl[(trimethylsilyl)methyl]ammonium Halides 3 yield from R' R2 x 2, 70 3a H H Br 93 3a' H H c1 92 3b Me H Br 92 3c H Me Br 80 OAc Br 81 3d H 3e c1 H c1 90 3f H c1 c1 81 I 900 3g COMe H 3h CN H Br 83 CN Br 91 3i H H Br b 3j NO2 NO, Br b 3k H
1979.44. -, - - ,2348. ~~~
~~
(3) Brasen, W. R.; Hauser, C. R. Organic Synthesis; Wiley: New York, 1954; Vol. 34, p 61. (4)Beard, W. Q., Jr.; Hauser, C. R. J. Org. Chem. 1960,25,334; 1961,
0022-3263/87/1952-l844$01.50/0
5
4
(1) (a) Johnson, A. W. Ylide Chemistry; Academic: New York, 1966; Chapter 7. (b) Pine, S. H. Organic Reactions; Wiley: New York, 1970; Vol. 18, Chapter 4. (c) Lepley, A. R.; Giumanini, A. G. In Mechanisms of Molecular Migrations; Thyagarajan, B. S., Ed.; Wiley-Interscience: New York, 1971; Vol. 3, p 297. (d) Kaiser, E. M.; Slocum, D. W. In Organic Reactive Intermediates; McManus, S. P., Ed.; Academic: New York, 1973; Chapter 5. (e) Zugravescu, I.; Petrovanu, M. N-Ylid Chemistry; McGraw-Hill New York, 1976; Chapter 2. (2) (a) Pine, S. H.; Munemo, E. M.; Fillips, T. R.; Bartolini, G.; Cotton, W. D.; Andrews, G . C. J. Org. Chem. 1971,36,984. (b) Bumgardner, C. L.; Hsu, H.-B.; Afghahi, F.; Robert, W. L.; Purrington, S. T. J . Orp. Chem.
26, 371. (5) Puterbaugh, W. H.; Hauser, C. R. J. Am. Chem. SOC.1964, 86, 1108. (6) (a) Sato, Y.; Sakakibara, H. J. Organomet. Chem. 1979, 166, 303. (b) Sato, Y.; Yagi, Y.; Kato, M. J. Org. Chem. 1980, 45, 613. (7) Vedejs, E.; Martinez, G. R. J . Am. Chem. Soc. 1979, 101, 6452.
2
1
a
Yield from 5 . *Not isolated.
amino)methyl]trimethylsilane (2). (2-Acetylbenzy1)dimethyl[(trimethylsily1)methyllammonium iodide (3g)was
0 1987 American Chemical Society
(Substituted benzy1)trimethylammonium Ylides in Nonbasic Medium Table 11. Reaction of Benzyldimethyl[(trimethylsilyl)methyl]ammoniumBromide (3a) with the Fluoride Anion products (7 and 8)
Fentry source 1 TBAF 2 TBAF 3 CsF 4 CsF 5 CsF 6 CsF 7 CsF
reactn total ratio" solvent time, h yield, % 7 to 8 38 61 97:3 THF 98:2 HMPA/THF (1:3) 17 74 15 84 97:3 HMPA MezSO 15 54 99:l Me2SO/THF (1:2) 15 62 99:l DMF 18 61 98:2 MeCN 15 tr
nThe ratio was determined by GLC analysis (10% PEG 20M).
Table 111. Reaction of (Substituted benz~l)dimeth~l[(trimeth~lsil~l)meth~llammonium Halides 3 with Cesium Fluoride
entry 1 2
3 4 5 6 7 8 9 10 11 12
13 14
3a 3a' 3a' 3a' 3b 3c 3d 3e 3f 3g 3h 3i 3j 3k
reactn time, h 15 44 122 2Od
25 25 22
25d 23d 24 24 25 24 24
products (7 and 8) bp,O OC % yieldb ratio' (mmHg) from 3 from 1 7 to 8 130 (150) 84 81 97:3 29 99:1 62 98:2 75 99:l 135 (155) 84 96:4 96:4 135 (150) 77 170 (20) 72 99:l 69 94:6 140 (105) >99:
