A comparison of the reactions of [(phenylthio)(trimethylsilyl)methyl]lithium with .alpha.,.beta.-unsaturated ketones and those of other acyl anion equivalents containing sulfur

Abstract

The factors influencing the site of attack of [ (phenylthio)(trimethylsilyl)methyl]lithium (1) with enones were investigated. Cyclohexenone (2) was chosen as a model compound, and conjugate addition occurred in THF-HMPA or DME; this mode of addition was also promoted by a potassium counterion. When the reaction was carried out with other enones, conjugate addition in THF-HMPA or DME was only observed if the P-position or the a,p-unsaturated ketone was not disubstituted. 1,4-Addition of 1 could be accomplished by preparation of the cuprate. The use of this approach was illustrated by a preparation of 4,4-dimethylcyclopent-2-en-l-one (28). For determination of the influence of DME on the regiochemical control of the addition of other sulfur-containing anions to enones, the study was extended to the anions derived from 1,3-dithian (29), bis(pheny1thio)methane (30), bis(phenylthio)(trimethylsilyi)methane (35), and bis(trimethylsilyl)(phenylthio)methane (36). With these anions, DME did not promote conjugate addition to any significant extent. (1) Parts of this work were carried out at the University of Southampton, for which an SRC postdoctoral fellowship is gratefully acknowledged, and the University 0 Rao, A. V. R.; Venkatawamy, G.; Javeed, M.; Deshpande, V. H.; Rao, B. R.

Enantioselective Total Syntheses of Citrinadins A and B. Stereochemical Revision of Their Assigned Structures

“…Additions of simple methyl-derived cuprates and related reagents proceeded with low (<2:1) diastereoselectivity. Similarly, the 1,4-additions of organocopper reagents derived from metalated bis(phenylthio)methane 15 and tris(phenylthio)methane 16 were rather unselective and also low yielding. After extensive experimentation, we eventually discovered that the organocopper reagent generated from (dimethylphenylsilyl)methylmagnesium chloride 17 and CuBr·DMS added smoothly to 38 in the presence of BF 3 ·OEt 2 to give a mixture of ketones that were directly reduced with high stereoselectivity using l -selectride to give 39 in 71% yield over two steps; 19% of the C(12) epimer of 39 was also isolated.…”

Conjugate Additions of Sulfur-Stabilized Anions to Unsaturated Lactams. Synthesis of Polyfunctionalized Benzo[a]quinolizinone Systems

“…For this purpose, we chose 2-lithio-1,3-dithiane and bis(phenylthio)methyllithium, which could show different behavior in conjugate additions . The latter anion would be more stable, whereas its acyclic structure allows rotation, optimizing orbital overlap with the conjugate acceptor . First, we studied the addition of bis(phenylthio)methyllithium to lactams 3a , b (Scheme , Table ).…”

Bis(phenylthio)methane

“…15 Lithio derivative (2) reacts with epibromohydrin by displacement of halogen, leaving the epoxide ring intact. 19 2-17 As exemplified in (eq 7), such reactions proceed readily.…”