Synthesis of Rings with One Other Heteroatom

Carbene reactions are of virtually no synthetic importance for silicon-containing heterocycles, mostly because of the poor selectivity of the carbene insertion processes involved. Thus cyclization of carbene 475 may be effected via Caikyi Si, Caryi Si and C—H bond insertions as well as via 

By Cu-catalyzed decomposition of ortho-seleno- and -telluro-substituted oj-diazoacetophenones, Lohner and Praefcke 482 synthesized seleno- and telluro-3-coumaranones 483. This reaction with the participation of a free carbene generated by photolysis of 482 (Z = Te) gives unsatisfactory results (80JOM173). 

A new method for the synthesis of cyclic iodonium ylides 484 has been developed via Rh2(OAc)4-catalyzed decomposition of a-diazodicarbonyl compounds and intramolecular capture of carbenes by aryl iodides (93MI2). 

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