Application of (13)C NMR Spectroscopy and (13)C-Labeled Benzylammonium Salts to the Study of Rearrangements of Ammonium Benzylides.
Ylides generated from N-(cyanomethyl)-N,N-dimethyl-N-[alpha-(trimethylsilyl)benzyl]ammonium chloride (4) and fluoride anion afford the products of [1,2] shift 11 and [2,3] shift 13. Formation of product 13 shows that, in the presence of water from TBAF, rearrangements and [1,3]H shift in ylide intermediates become competitive processes. The reaction of N-benzyl-N,N-dimethyl-N-[alpha-(trimethylsilyl)benzyl]ammonium bromide (5) and (13)C labeled (at the benzyl carbon) salt 5 gave a mixture of 10, 14, and 15 as products of [1,4], [1,2], and [2,3] rearrangement, respectively. (13)C NMR spectra of products derived from salt 5 exclude [1,3]H shift in ylide 9a(+-)(). Rearrangement of ylides generated from N-benzyl-N,N-dimethyl-N-[(dimethylphenylsilyl)methyl]ammonium bromide (6) (enriched in (13)C at benzyl carbon) and n-BuLi reveals that N,N-dimethyl-2-[(dimethylphenylsilyl)methyl]benzylamine (20) is not formed by a [1,4] shift but instead, via a [2,3] shift in silylmethylide followed by subsequent [1,4]Si and [1,2]H shift, as previously suggested in the literature. This mechanism is unique to some silyl-substituted ylides.
Zdrojewski
Tadeusz
T
Faculty of Chemistry, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland.
Jonczyk
Andrzej
A