1 -Alkylidenelactones

Alkylidene lac tones.1 The alkenylpalladium(II) intermediate obtained in the reaction of lithium alkynoates with PdCl2(CH3CN)2 (12, 50) can be trapped with allyl halides to give (E)-alkylidenelactones. 

Very powerful synthetic strategy for the synthesis of a-alkylidenelactones and lactams 115 relies on the Horner-Wadsworth-Emmons (HWE) or Wittig reaction where the corresponding a-dialkoxyphosphoryllactones and lactams or ylides 114 are reacted with carbonyl compounds 24a resulting in the introduction of the alkylidene moiety (Scheme 4.30) [2a]. Consequently, development of the synthetic methods for the efficient preparation of 114 has recently received considerable attention. 

The convenient synthetic methodology for the a-silyl esters has been ejrtended to the synthesis of a-alkylidenelactones [198, 199]. Peterson reactions of the carban-ion generated from a-silyl-y-butyrolactones 117 with carbonyl compounds afford the corresponding a-alkylidene-y-lactones 118 with high -selectivity (Scheme 2.71). The yields are low when ketones are used as substrates. 

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