Cyclobutanols, 2- rearrangement oxyanion-accelerated

Bauld and coworkers have examined the cation radical cycloadditions of 1,3-dienes with electron-rich alkenes and found that, under photosensitized electron-transfer conditions, [2 -i- 2] cycloaddition is in many cases favored over Diels-Alder addition. Thus, as illustrated in equation (30), 1, T-dicyclopentenyl (186) reacts with p-chloroethyl vinyl ether under electron transfer conditions to afford the cyclobutane adduct (187), which was cleaved to the cyclobutanol (188) in 70% yield upon treatment with n-butyl-iithium. Oxyanion-accelerated VCB rearrangement then provided (189) as a mixture of diastereomers in... 

The chemistry of the divinylcyclobutanols derived from 5-methylenespiro[3.5]nonanone (260) proved to be more complicated than the reactions described above. As expected, the oxyanion-accelerated 3,3-sigmatropic rearrangement of the cis isomer (261) was extremely f acile as a consequence of the rigid j-cis orientation of the exocyclic methylene group (Scheme 35). The rearrangement of the trans isomer, however, produced none of the desired Cope product instead this cyclobutanol salt underwent exclusive 1,3-rearrangement to afford the cyclohexenol derivative (264). It is uncertain whether this transformation... 

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