The chemistry of .alpha.-silyl carbonyl compounds. 17. Methyldiphenylsilylation of ester and lactone enolates

Abstract

The reactions of a variety of ester and lactone enolates with methyldiphenylchlorosilane were studied. The Cversus O-silylation, leading to the -silyl ester or lactone and silyl ketene acetal, respectively, was studied as a function of the structure of the ester or lactone and the reaction conditions. It was found that all simple acetates are C-silylated irrespective of the steric demands of the alcohol portion of the ester. Esters that are monosubstituted in the -position are cleanly C-silylated with the notable exceptions of ethyl phenylacetate and ethyl phenoxyacetate, both of which give mixtures of C-and O-silylation. The , -disubstituted esters give only O-silylation, but the a,«-substituted -silyl esters are readily prepared by the alkylation of the appropriate monosubstituted -silylated ester. The reaction of the lithium enolate of ethyl acetate and ierf-butyl acetate with (S)-(-)-l-naphthylphenylmethylchlorosilane showed the reaction to occur with inversion of configuration at silicon. Methylation of fert-butyl (1 -naphthylphenylmethylsilyl)acetate gave a 91:9 mixture of diastereomeric -silyl propionates, which could not be separated. It was found that only the y-lactones gave C-silylation with -valerolactone and e-caprolactone giving O-silylation.The silylation of ester or lactone enolates can occur to produce the silyl ketene acetals or the -silyl esters or lactones, all synthetically useful classes of compounds, as a result of silylation at the Oor C-terminus of the enolate

Sodium Aminotroponiminates: Ligand‐Induced Disproportionation, Mixed‐Metal Compounds, and Exceptional Activity in Polymerization Catalysis

“…A deprotonative initiation mechanism has previously been suggested for reactions with Na(C 5 H 5 ) on the basis of end group analysis . This is also in line with reports of NaNH 2 and LiN( i Pr) 2 reacting with enolizable organic esters (including ϵ‐CL) via deprotonation rather than nucleophilic substitution (i. e. amide formation) ,…”

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

“…In enolate reactions, but with chiral silicon, a surprisingly high level of control has been found in the methylation 1923 → 1924 (Scheme ) and the vinyllithium reagent derived from the bromide 1927 was completely unselective (Scheme ).…”

Synthesis and Applications of Unquaternized C-Bound Boron Enolates

“…Amides undergo O-to-C isomerization even more readily than esters, and do not even require particularly nucleophilic phosphine to induce the isomerization. This can be attributed to the greater resonance delocalization of amides compared to esters, resulting in stabilization of the carbonyl group and therefore a higher preference for C-boron enolate formation . Consistent with this trend, attempts to generate C-boron enolates from O-boron enolates of ketones were unsuccessful…”