Gold-catalysed generation of diol equivalents from epoxides and their intramolecular reaction with C≡C bonds to generate bicyclicketals is presented. This reaction essentially involves the formation of an acetonide, which subsequently cyclises on the alkyne intramolecularly under gold catalysis conditions. This method could be extended to make optically pure bicyclicketals. Deuterium incorporation
Cyclisation of terminal epoxy bis-sulphones can occur in two different modes; rates of ring closure for three- to seven-membered rings span over three orders of magnitude.
末端环氧双砜的环化可以两种不同的方式发生。三元至七元环的闭环速率跨越三个数量级。
BENEDETTI, FABIO;BERTI, FEDERICO;FABRISSIN, SILVIO;GIANFERRARA, TERESA;RI+, J. ORG. CHEM., 56,(1991) N1, C. 3530-3537
A quantitative study on the effects of methyl and gem-dimethyl groups in the intramolecular ring opening of epoxides by bis-sulfonyl carbanions is reported for the formation of cyclopropanes. Reaction rates are increased by methyl groups on the chain connecting the nucleophile with the oxirane and depressed by methyl substitution in the epoxide ring. When gem-dimethyl groups are present on the epoxide, ring opening is apparently inhibited. It will be shown that in this case the reaction is reversible and the apparent stabilization of the gem-dimethyl-substituted oxirane is actually due to a combination of effects on both the forward and the reverse reactions. On the basis of current theories on intramolecular reactions, it is suggested that release of ground-state strain and van der Waals repulsions in the transition state can account for the observed reactivity.