Inverto-yuehchukene

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. 

Examples do exist however, of productive Nazarov cyclizations bearing electron-rich heteroatoms in the P-position. For example, cyclization of substrate 60 (albeit with the nitrogen atom contained within an aromatic indole moiety) was reported by Cheng and co-workers in 1996. Exposure of 60 to HCl in refluxing dioxane resulted in the formation of product 61 in moderate yield. This key intermediate was then transformed into inverto-yuehchukene (62), a dimer of 2-didehydroprenylindole. 

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