Syntheses with metallated thioacetals and orthothioformates

Abstract

AbstractThioacetals and orthothioformates, compounds having the general formula HC(R)(SR′)2 with R = H, SR′, CH3, or C6H5 and R′ = C2H5 or C6H5, were metallated by means of alkali amides in liquid ammonia. The metallated derivatives were A) alkylated, B) converted with ketones (successfully only when R = H and R′ = C6H5), and C) ethylthiolated by means of diethyldisulphide (only when R = H, SR′, or C6H5). The results of the reactions are summarized in Tables I‐VI, VIII, and IX. Similar conversions were impossible with common acetals or orthoformates (notably CH2(OC2H5)2, C6H5‐CH(OC2H5)2, and CH(OC2H5)3). The easy metallation of the thiocompounds is attributed to d‐orbital participation of sulphur, which probably lowers the activation energy of the metallation reaction and enhances the stability of the carbanions.The new reactions in principle enable the synthesis of aldehydes from formaldehyde, of methyl ketones from acetaldehyde, of phenyl ketones from benzaldehyde, and of carboxylic acids from formic acid.Upon standing, solutions of NaC(SC2H5)3 and NaC(SC6H5)3 in liquid ammonia slowly decompose, yielding compounds of the type (R′S)2C = C(SR′)2. The transient occurrence of a carbene: C(SR′)2, formed by splitting‐off of thiolate from the carbanion ⊖ C(SR′)3, is discussed.