Gold(I)-catalyzed ring expansion of cyclopropanols and cyclobutanols.

The rearrangement of 1-alkynyl cyclobutanols and cyclopropanols to alkylidene cycloalkanones catalyzed by cationic triarylphosphine gold(I) complexes is described. The reaction tolerates terminal alkynes as well as alkyl, aryl, and halo-substitution at the acetylenic position and stereoselectively provides a single olefin isomer. The gold(I)-catalyzed rearrangement is stereospecific with regard to substituents on the ring, thus providing a practical method for the stereoselective synthesis of highly substituted cyclopentanones from cyclopropanols. The reaction stereoselectively provides a single olefin isomer and is stereospecific with regard to substituents on the ring via sequential gold(I)-catalyzed ring expansion reactions.

Catalytic isomerization of 1,5-enynes to bicyclo[3.1.0]hexenes.

The cycloisomerization of 1,5-enynes catalyzed by cationic triphenylphosphinegold(I) complexes produces bicyclo[3.1.0]hexenes. Substitution at all positions of the 1,5-enyne is tolerated, leading to a wide range of bicyclo[3.1.0]hexane structures, including those containing quaternary carbons. Substrates containing a 1,2-disubstituted olefin undergo stereospecific cycloisomerization (cis-olefin produces cis-cyclopropane, and trans-olefin gives trans-cyclopropane). Additionally, enantioenriched bicyclo[3.1.0]hexenes can be obtained from the gold(I)-catalyzed cycloisomerization of enantioenriched 1,5-enynes with excellent chirality transfer. The preparation of tricyclic systems is accomplished through a gold(I)-catalyzed tandem cycloisomerization-ring enlargement reaction.