We report the enantioselective, lateral deprotonation of ortho-protected or functionalized tertiary N,N-dialkyl aryl O-carbamates 5-7 (Scheme 2 ) and meta-protected carbamates 14, 15, and 20 (Schemes 5 and 7 ) by s-BuLi/(-)-sparteine and subsequent quench with a variety of electrophiles to give products 11-13 and 16, 17, and 21 in yields up to 96% and enantiomeric ratios up to 99:1. The influence of organolithium reagents, ratio of organolithium/(-)-sparteine pair versus N,N-dialkyl aryl O-carbamate starting materials, temperature, solvents, electrophiles, substituents located ortho or meta to the O-carbamate moiety, and O-carbamate N-substituents was investigated. The identical absolute configuration of the stereogenic center of the major enantiomers of the products, as established by single-crystal X-ray analysis for substrates (S)-11c, (S)-19, and (S)-21a, provides evidence for a consistent stereochemical course in the enantioselective deprotonation. Mechanistic investigations, including an estimate of the configurational stability of the benzyllithium species 9 (starting from 12e; Scheme 8 ) and 23 (starting from 17e; Scheme 9 ), both derived by tin-lithium exchange, and 24 (starting from 20; Scheme 9 ) are reported. The experimental results, together with semiempirical molecular orbital calculations (PM3/SMD), are consistent with a process in which enantioinduction occurs in the deprotonation step (Scheme 11 ).

The 3 J( 29 Si, 1 H)-coupling constants of a number of vinylsilanes have been accurately determined with the ACT-J-NMR experiment. For all investigated samples the values of the 3 J trans -coupling constants were found to be significantly larger than the corresponding values of the 3 J cis -coupling constants (8.8-20.5 Hz versus 3.1-11.9 Hz). Since substituent effects were characterized over a wide range, a conclusive assignment of the double-bond geometry of a particular vinylsilane by means of a single 3 J( 29 Si, 1 H)-coupling constant is now possible even though the ranges of the 3 J cis -and the 3 J trans -values overlap.

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where a hydride is proposed to be transferred from the benzyl position to a neighboring thionium ion. This would form a particle that could readily lose benzaldehyde as a neutral fragment. The CI-MS results provide an explanation for the unusual instability of (benzy1oxy)methyl-substituted silanes towards acids. In fact, the fonnation of benzaldehyde was established in the decomposition of a (benzy1oxy)metbyl-substituted acylsilane in the presence of Lewis or Brensted acids and ethanethiol. The CI-MS study, therefore, represents a useful method to recognize unusual reactions that are -or might be -important in solution.