Cheng indole synthesis

A simple two-step protocol for the generation of a terminal diene is to add allyl magnesium bromide to an aldehyde or a ketone and subsequent acid or base catalysed dehydration (equation 34)72. Cheng and coworkers used this sequence for the synthesis of some indole natural products (equation 35)72a. Regiospecific dienones can be prepared by 1,2-addition of vinyllithium to a,/l-unsaturated carbonyl compounds and oxidative rearrangement of the resulting dienols with pyridinium dichromate (equation 36)73. 

Cheng and Cheung also employed a 2-indolylzinc chloride 72 to couple with indole 71 in a synthesis of "inverto-yuehchukene" 73 [104]. Other Pd catalysts were no better in this low-yielding process. 

Kong, Y. C. and Cheng, K. F. 1989. Yuehchukene analogs and derivatives and related indoles, useful as female fertility-regulatmg agents, their synthesis, and pharmaceutical preparations. Brit U. K. Pat Appl. GB 2207670 A 19890208. 

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