[3,3]-Sigmatropic Rearrangement/5-exo-dig Cyclization Reactions of Benzyl Alkynyl Ethers: Synthesis of Substituted 2-Indanones and Indenes

Substituted benzyl alkynyl ethers, prepared from the corresponding alpha-alkoxy ketones in a two-step sequence involving enol triflate formation and KOtBu-induced E2 elimination, undergo [3,3] -sigmatropic rearrangement/intramolecular 5-exo-dig cyclization at 60 degrees C to form substituted 2-indanones in good overall yields. 1,3-cis-Disubstituted-2-indanones are formed preferentially when the benzylic substituent R-1 is bulky. Substituted indenes may be prepared from 2-indanones in high yields by Horner-Wadsworth-Emmons reaction.