Recent Advances in the Synthesis of 2H-Pyrans.

In this review, we discuss the nature of the different physicochemical factors affecting the valence isomerism between 2H-pyrans (2HPs) and 1-oxatrienes, and we describe the most versatile synthetic methods reported in recent literature to access to 2HPs, with the only exception of 2HPs fused to aromatic rings (i.e., 2H-chromenes), which are not included in this review.

Synthesis and Utility of 2,2-Dimethyl-2 H-pyrans: Dienes for Sequential Diels-Alder/Retro-Diels-Alder Reactions.

The practical use of 2,2-dimethyl-2 H-pyrans as electron-rich dienes in sequential Diels-Alder/retro-Diels-Alder (DA/rDA) domino processes to generate aromatic platforms has been demonstrated. Different polysubstituted alkyl 2-naphthoates have been synthesized by the DA/rDA reaction of benzynes and 2,2-dimethyl-2 H-pyrans. The use of other activated alkynes allows the access of substituted alkyl benzoate derivatives.