Investigation of an electrocyclisation route to the 7bH-cyclopent[c,d]-indene system
Abstract
An approach to the synthesis of derivatives of 7bH-cyclopent[cd]indene ring system (1) has been explored in which two of the three rings are constructed by cyclisation reactions. The acetylenic alcohol (7) was prepared by coupling of 3-iodo-2-methylcyclopent-2-en-1-one (6) with the copper(I) salt of prop-2-ynyl alcohol tetrahydropyranyl ether. This was then converted into the Z,E-trienedione (2). On heating, this compound failed to undergo cyclisation; the only reaction observed was its isomerisation to the E,E-trienedione (10). Under forcing conditions it gave only indan -1-one.
The cis-double bond of the trienedione system was fixed by incorporating it into a bicyclo[2.2.1]heptadiene system. Two such derivatives, (14) and (15), were prepared; both underwent smooth electrocylic ring-closure on heating and the ylide (15) also cyclised further to give compound (19), which incorporates the required 7b-H cyclopent [cd]indene skeleton.