Y-Lactones enolates

The utility of the creation of a y-lactone enolate through 1,4-addition of a carbanion and its interception by an electrophile has also been demonstrated in other classes of natural products, e.g., in the enantioselective synthesis of 10-oxa-l 1-methyl PGE2 analogues22. This synthesis starts with 1,4-addition of the sulfone-stabilized anion from 27 to ( + )-(S )-4-methyl-2-buteno-lide which has been prepared in three steps from (—)-(S)-l,2-epoxypropane. The intermediate enolate 28 is reacted with the acetylenic iodide to give the trisubstituted diastereomeric mixture of lactones 29, which is eventually converted into the pure compound 30, both reactions occurring with high diastereoselectivity. 

Intramolecular alkylations of y-lactone enolates are merely variants of the examples mentioned in the previous sections (Section 1.1.1.3.2.2.1.). A striking feature of these reactions is their efficiency with mild bases such as l,8-diazobicyclo[5.4.0]undec-7-ene (DBU) or potassium er -butoxide instead of the lithium amides. 

The reaction of esters and y-lactone enolates with diphenylmethylsilyl chloride is reported to be atypical and to give the C-silylated product (Scheme 11). ... 

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