Site-specific reactions of trimethylsilyl enolates and trimethylsilyldienolates are described. Recently some reactions of the Eschenmoser salt, ,J', with enolates2'3'4, Grignard5a and lithium5b reagents were described. This methodology was used to some advantage in a synthesis of vernolepin.6 A more detailed study was provided by Holy.' In our preliminary experiments* we also noted that compound 1 is sufficiently electrophilic to react with trimethylsilyl enol ethers. This process was used in the synthesis of a known precursor of dl-progesterone. We now describe a fuller examination of the reactions of 1 with trimethylsilyl enol ethers. In particular we were attracted by the possibility of exploiting such methodology to address the longstanding problem of regiospecificity in the Ma:iagh Reaction.8a While some solutions to this problem have been advanced in the litera-, the possibility of obtaining positionally defined Mannich bases via positionally defined silyl enol ethers' seemed most attractive. Treatment of 1-trimethylsilyloxy-2-methylcyclohexene (5) with the iodide, 2, at room temperature for 45 min followed by acidic workup and basification afforded a 65% yield of a Mannich base. Singlet resonances for the quaternary bound methyl group ~1.1 (s, 3) and for the NCH2 protons ~2.54 (s, 2) served to define the structure of the Mannich base as $0 Similarly, reaction of ,4 with J, afforded a 79% yield of ,5 as a 2:1 mixture of stereosiomers. With both 2 and ,5 in hand, it was possible to probe the regiospecificity of the reactions of & and ,4 with 1 in greater detail. Within the limits of nmr detection at 250 MHz, we could find no indication that any component of isomer mixture ,5 had risen in the reaction of2 + 3. However, there could be detected ca 4% of .J in the reaction of -J '2.
Since starting silyl enol ether ,4 was free of detectable amounts of its isomer,