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The substituted methyl cinnamates 4 and 5 have provided a unique system for the study of various mechanistic aspects of the nucleophilic 1,4 addition of sodium borohydride to ,/3-unsaturated esters. Competitive rates of reduction for two sets of methyl a-phenyl-trores-cinnamates (4), para-substituted in the a and ß rings, respectively, correlate linearly with Hammett values. The similarity in pa (1.74) and ps (1.44) indicates that the transition state for hydride transfer occurs before significant change in geometry of the ,/3-unsaturated carbonyl system occurs. Competitive rate studies for methyl a-(para substituted phenyl)acrylates (2) and methyl of-phenyl-a's-and -trans-crotonates (14 and 15) are corroborated by the data obtained for the cinnamates.Carbon-carbon double bonds conjugated with strong anion-stabilizing groups (e.g., COR, CO2R, CN, SO2R, NO2) have occasionally been observed to undergo reduction with sodium borohydride.2-11 Although it is recognized that sodium borohydride exhibits nucleophilic behavior,3-4 little is known concerning the mechanism or even the general structural requirements for the occurrence of such reactions.

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Addition reactions O 0060Trans Dialkoxylation of Cyclic Alkenes: A Prevost-Type Reaction. -The one-step method for trans-1,2-dialkoxylation of cyclic alkenes occurs via initial formation of the trans-iodoethers, which undergo Ag-assisted iodide abstraction to afford the trans-diethers. The combination of silver perchlorate, collidine, and iodine in 2:1:1 molar ratio is of importance, since this mixture is effective for conversion of cyclic alkenes to trans-diethers. Cyclic alkenes possessing unsubstituted carbon-carbon double bonds provide diethers in high yields and purity while alkenes with trisubstituted double bonds furnish lower yields of diethers, accompanied by side products. -