Utilization of Transition-Metal Carbenoids

Transition-Metal-Mediated Aromatic Ring Construction, First Edition. Edited by Ken Tanaka, 2013 John Wiley Sons, Inc. Published 2013 by John Wiley Sons, Inc. 

Carbene complexes have proven to be highly useful in the constmction of pyrrole and furan ring systems. Very often these processes result in unique disconnections to these ring systems that have no parallel in classical organic chemistry. Specific examples are depicted in the following sections. 

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Transition metal catalyzed decomposition of unsaturated a-diazo ketones or a-diazo esters is a powerful method for the synthesis of certain 2-oxobicyclo[n.l.0]alkanes. In contrast to the thermal (see Section 1.2.1.2.4.2.6.1.) and photochemical (see Section I.2.I.2.4.2.6.2.) methods, which have only been applied successfully in a few cases, the carbenoid version has been extensively utilized for the construction of simple or highly substituted bicyclic, tricyclic or higher systems of predictable stereochemistry (for reviews, see refs 2, 82, 320). Several of the cyclopropanes so obtained have been transformed further into natural products with diverse molecular skeletons. As examples and procedures have already been presented in Houben-Weyl, Vol. E19b, ppl088ffand 1271 ff, only some important aspects concerning the scope and limitation of the method as well as recent developments concerning its stereochemistry will be discussed here. 

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