Cyclopentanones vinylcyclopentanones

CYCLOPENTANONES FROM CARBOXYLIC ACIDS VIA INTRAMOLECULAR ACYLATION OF ALKYLSILANES 2-METHYL-2-VINYLCYCLOPENTANONE... 

R Cyclopentanones from Carboxylic Acids via Intramolecular Acylation of Alkyl silanes 2-Methyl-2-vinylcyclopentanone... 

A photochemical route to racemic estrone commencing with 2-bromo-5-methoxytoluene depended upon the generation of a quinodimethane intermediate incorporating an enolic component (ref. 129). Subsequently the method was adapted to furnish an asymmetric synthesis of (+)-estrone as described in the ensuing section. The cyclopentanone component was derived by the reaction of dimethyl malonate with E-1,4-dibromobut-2-ene to give racemic dimethyl 2-vinylcyclopropane-1,1-dicarboxylate which was then transformed by reaction with dimetyl methylmalonate followed by hydrolysis into racerruc 2-methyl-3-vinylcyclopentanone. 

Posner has also described the stereocontrolled addition of vinyl Grignard reagents to enantiomerically pure cyclopentanone sulfoxides [43,47]. The addition of vinylmagnesium bromide to (70) pre-complexed with zinc bromide, and further reaction as described in Scheme in 4.36, yielded exclusively (5,5)-3-vinylcyclopentanone (71) in 30% overall yield. 

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