A DFT-Based Analysis of the Gold-Catalyzed Cycloisomerization of 1-Siloxy 1,5-Enynes to Cyclohexadienes.

In this work, we present a deep theoretical study on the intriguing and unexpected gold-catalyzed cycloisomerization of siloxy enynes to cyclohexadienes. To this end, we have evaluated the electronic and steric properties for three types of alkynyl substituents along the reaction paths and the implications on the evolution through divergent, competitive pathways. For an alkynyl -OR substituent, the results strongly suggest a polarization of the π electrons along the delocalized C2-C1-O system in the key cyclopropyl-carbene intermediate, which is enhanced by the bulkiness of the R group. The results reproduce the experimental observations in excellent agreement and provide interesting and useful clues for predicting the effects of the alkynyl substituent on the nature of the key intermediate and, hence, on the reactivity mode and selectivity. [ABSTRACT FROM AUTHOR]