Alkaloid Synthesis via Carbenoid Intermediates

Carbene and metal carbenoid species, originally viewed as too reactive to be useful for complex molecule synthesis, have now emerged as attractive intermediates for the construction of highly functionalized heterocyclic compounds. A popular route to metal carbenoids involves the decomposition of diazo starting materials, using various transition metals. In this review we highlight some of the utilities of metal carbenoids in the synthesis of biologically-active or natural product-like compounds. Some of the reaction classes that feature prominently in these syntheses of alkaloids, described here, involve heteroatom/C-H insertion or cyclopropanation and 1,3-dipolar cycloadditions. The facile constructions of fused ring systems via cascade reactions that encompass carbenoids are also discussed.