Sulphone-mediated cyclobutanone to α-alkoxy-cyclopentanone ring expansion reactions; scope, limitations and applications

Article abstract of DOI:10.1016/S0040-4020(01)85603-9

The bicycloalkanones (1)-(3) were treated with the lithiated sulphone (4) to give the ring expanded α-methoxyketones (12), (14) and (16) generally as a mixture of epimers. The same bicycloalkanones furnished the α-benzyloxyketones (13), (15), and (17) on reaction with reagent (5). The ketone (3) reacted with the sulphone anion (6) to give, after Lewis acid treatment, the α-allyloxycyclopentanone derivatives (27a) and (27b) and one of these compounds (27b) was transformed into the ether (31). The bicycloheptanone (20) was converted into four ring-expanded products (22a), (22b), (24a) and (24b) and one of the compounds (24a) was used to synthesise the prostacyclin analogue (36). A brief study was made of the mechanism of the Lewis-acid catalysed rearrangement of the intermediate hydroxy sulphone to the ring-expanded compounds.