Alkylidene malonates olefination

The most reactive Michael acceptors, such as alkylidene malonates, gem-dicyanoalkenes and nitroalkenes, react with a-halozinc esters in a conjugate fashion. Beautiful examples were offered by two stereocontrolled conjugate additions to piperidinone 102 and pyrro-lidinone 104 leading to optically active bicyclic lactams 103147 (equation 60) and 105 (equation 61)148. With these electron-poor alkenes a Grignard two-step protocol is to be adopted in order to avoid the single electron transfer reactions from the metal to the Michael acceptor, which should afford olefin dimers. The best solvent is found to be a... 

An alternative complementary olefination procedure involving alkylidene malonates was also developed that produces (Z) olefins as major stereoisomers when the R substituent is aliphatic (equation 93)130. The stereoselectivity depends on the bimetallic compounds and may be improved by bulky ester substituents (such as menthyl groups)131. 

Dibutyl telluride 59 reacts with iodomethyl triphenylphosphonium iodide to give triphenylmethylidene phosphor-ane, which reacts with aldehydes leading to the methylenation products in good yields.119 The same reagent 59 also assists the reaction of dibromomalonates 60 with aldehydes and activated olefins affording alkylidene malonates 61 and cyclopropanes 62 derivatives, respectively (Scheme 30). 

Catalytic direct asymmetric Michael reactions Addition of unmodified ketone and aldehyde donors to alkylidene malonates and nitro olefins." Synthesis, No.9, Qun 18, 2004), pp. 1509-1521, ISSN 0039-7881... 

The RCM reactions of malonates have been defined as benchmark substrates for olefin metathesis catalysts [20]. The productive pathway begins with a crossmetathesis reaction to generate an alkylidene intermediate with a pendant olefin. A second, intermediate metallacycle is generated by the intramolecular addition of this pendant moiety, which subsequently releases the cyclized product and an equivalent of ethylene (Scheme 10.18). 

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