The unprecedented reaction of dimethylsulfonium methylide with Michael acceptors: synthesis of 1-substituted vinyl silanes and styrenes

Abstract

Rather than the usual cyclopropanation, conditions for an unprecedented elimination reaction from the adduct of dimethylsulfonium methylide and various Michael acceptors have been established leading to functionalized 1-substituted alkenes. In silyl substituted substrates (2a and 2h), where a facile Peterson-type olefination is possible from the adduct; elimination took place instead to give functionalized 1-substituted vinyl silanes. Aryl substituted Michael acceptors (2b-e, 2g and 2i-k) also underwent a similar kind of olefination to give 1-substituted styrene derivatives with moderate yields along with a side product, which arose by nucleophilic demethylation from the adduct of dimethylsulfonium methylide and arylidene malonates. Hammett studies revealed that selectivity for olefination vs. demethylation increases as the aryl substituent becomes more electron deficient. Alkylidene malonates (2f and 2l) with a beta-alkyl substituent did not favour the olefination process. Sequential addition of Michael acceptors and alkyl halides to a mixture of dimethylsulfonium methylide and sodium dimsylate provided olefination followed by alkylation on the active methine group. A mechanistic pathway has been formulated from the studies of a few sulfonium methylides.

Tuning the Stability and the Reactivity of Substituted [3]Dendralenes for Quick Access to Diverse Copiously Functionalized Fused Polycycles with Step and Atom Economy

“…We in our group were engaged in the synthesis of [3]­dendralenes for a couple of years, utilizing a sequential olefination methodology by employing dimethylsulfonium methylide. Initially, the dienylphosphonoacetates I were converted to dendralenes II by a Horner–Wadsworth–Emmons (HWE)-type olefination, but the terminally aryl-substituted [3]­dendralenes produced were so unstable that they underwent a rapid in situ cyclodimerization to provide highly functionalized cyclohexenes III with excellent regio- and stereocontrol (Scheme ).…”

Silicon assisted diversified reaction of a β-silylmethylene malonate with dimethylsulfoxonium methylide

“…n-BuLi (1.5 M in hexane), Me 3-S(O)I and Me 3 SI were purchased from Aldrich. Compounds 2a and 2d were prepared following our reported procedure [46]. The column chromatography was performed on silica gel (230-400 mesh).…”

“…Recently, we and others have shown that dimethylsulfonium methylide (DIMSY) (1) when used in excess, or in the presence of a base can act as an equivalent of a carbenoid to produce interesting product(s) when reacted with various Michael acceptors [45][46][47][48][49][50][51][52], activated dienes [53], carbonyl compounds, imines and epoxides [54][55][56][57]. For example, when DIMSY was reacted with b-silylmethylene or b-arylmethylene malonates 2, cyclopropane derivatives 3 or olefins 4 were obtained [45][46][47][48][49][50][51][52] depending upon the quantities of the ylide and base used (Scheme 1).…”

Enantioselective Route to β-Silyl-δ-keto Esters by Organocatalyzed Regioselective Michael Addition of Methyl Ketones to a (Silylmethylene)malonate and Their Use in Natural Product Synthesis

“…15 However, such types of reactions have not been applied to the synthesis of b-silyl-d-keto esters. We envisage an alternate and straightforward method that involves an atom-economic, 16 regio-and enantioselective, direct Michael addition of an alkyl methyl ketone to the bsilylacrylate 4 or (silylmethylene)malonate 5 17 (Figure 1). The Michael addition 18 is one of the most frequently used reactions because of its efficiency and effectiveness.…”

“…Silylmethylene malonate 5 was prepared following a procedure reported by us. 17 Diphenylprolinol 6a was commercially available and its TMS ether 6b was prepared according to the literature 37 procedure. All the amino acids were purchased from commercial sources.…”