Synthesis of oxygen-containing heterocyclic compounds based on the intramolecular O–H insertion and Wolff rearrangement of a-diazocarbonyl compounds

The addition products of Ti(IV)-enolate derived from b-keto a-diazo carbonyl compound to ketones or a,b-unsaturated compounds were subjected to Rh2(OAc)4-catalyzed and photo-induced diazo decomposition. The Rh2(OAc)4-catalyzed reaction afforded intramolecular O–H insertion products, while the photo-induced reaction gave Wolff rearrangement/intramolecular nucleophilic addition products. The transformations represent new approaches to tetrahydrofuran and c-butyrolactone derivatives. 2006 Elsevier Ltd. All rights reserved. Oxygen-containing heterocycles, especially tetrahydrofuran and c-butyrolactone derivatives, are important synthetic targets due to their occurrence in numerous natural products, their wide range of biological activities, and their utility as versatile intermediates in organic synthesis. In addition to the traditional methods, many new synthetic methodologies have been developed in recent years for this important class of heterocyclic compounds. In particular, transition metal catalyzed transformations have been successful and offer great potential. For example, platinum-catalyzed intramolecular hydroalkoxylation of c-hydroxy olefins led to the formation of tetrahydrofuran derivatives. Palladiumcatalyzed cyclization of allylic 2-alkynoates has been utilized to build c-butyrolactone derivatives. In this paper, we report a new approach to both tetrahydrofuran and c-butyrolactone derivatives based on the reaction of a-diazocarbonyl compounds. We have recently studied the nucleophilic addition of Ti(IV) enolate 2, derived from b-keto a-diazo carbonyl compound 1, to various electrophiles (Scheme 1). Although the efficient addition of Ti(IV) enolate 2 to aldehydes has already been reported by Calter and coworkers, we have found that the corresponding reac0040-4039/$ see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2006.05.007