1. Sigmatropic Rearrangements of Benzyl Alkynyl Ethers
Thomas G. Minehan, Department of Chemistry, California State University
Northridge, CA 91330
Low temperature sigmatropy: [3,3]-sigmatropic rearrangement of substituted benzyl alkynyl ethers at 60°C, followed by intramolecular 5-exo dig cyclization, gives rise to cis-disubstituted 2-indanones as major products. The larger the benzylic substituent R1 in the starting benzyl alkynyl ether, the greater the syn stereoselectivity (t-Bu>iPr>Me) of the reaction. Furthermore, ester-substituted 2-indanones (R2=CO2Et) may by transformed into substituted indenes in high yield by a two-step sequence involving enol triflate formation and palladium-catalyzed cross coupling reaction with arylindium reagents or arylboronic acids. Indenes and indanes form the core of numerous biologically active compounds such as indatraline.
Uncatalyzed sigmatropic rearrangements of allyl and benzyl alkynyl ethers take place at
low temperatures, allowing carbon-carbon bond-formation under relatively mild
reaction conditions. Since carbon-carbon bonds form the backbone of all organic molecules,
the reaction developed represents a highly useful means for the construction of complex
organic molecules.