Abstracr -Tertiary allylic alcohols derived from 1.2-addition of 2-lithio-4.5dihydrofuran to ketones are shown to be capable of conversion to dimeric spiro-l.4dioxaneror to monomeric ring-expanded spirocy~li~ ketones depending upon the conditions of acid catalysis employed.Allylic cations are easily generated in solution.Indeed, they are known to be stable in concentrated sulfuric acid provided that the terminal carbon atoms are fully alkylated.2A l - though the resonance energy of CH~-CH-CH~+ remains e l u s i ~e .~ its gas-phase heat of formation has been approximated to be 226 k c a l / m ~l .~ The ability of a hetero atom to stabilize positive 10.
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Paquette et al. (1990) studied this question.