A simple synthesis of the title compounds, which is more than 10 steps shorter and an order of magnitude more efficient than our recent photochemical synthesis of chasmanine, is described. The main feature of the new process is a stereo- and regiospecific addition of benzyl vinyl ether to an o-quinone intermediate masked by a spirolactone group according to the method of Deslongchamps.
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Wiesner et al. (1978) studied this question.