Use of oxygenated 1,3-dipoles for the synthesis of nitrogen containing heterocycles.

Over the past several decades, the 1,3-dipolar cycloaddition reaction has been successfully applied in alkaloid synthesis as a strategy to reduce the number of steps, increase overall yield and employ more easily available starting materials. This mini-review presents selected examples making use of substituted carbonyl ylides as 1,3-dipoles for the preparation of numerous nitrogenous natural products. The cycloaddition reactions of mesoionic oxazolium ylides (isomünchnones) are first discussed, wherein intramolecular reactions of these dipoles have been exploited as an approach to the ring system of several different alkaloids. The creation of carbonyl ylide dipoles from the reaction of α-diazo compounds with either ketones, esters or amides in the presence of Rh(II) catalysts has significantly broadened their applicability for natural product synthesis and is reviewed here. The cases presented demonstrate that a domino cascade strategy of these unique 'push-pull' dipoles may play a major role in shaping the future synthesis of complex nitrogen-containing natural products. [ABSTRACT FROM AUTHOR]