Intramolecular 4+3 cycloadditions. Allylic sulfones as precursors to vinylthionium ions

(5,6-Dihydro-1,4-dithiin-2-yl)methanol as a Versatile Allyl-Cation Equivalent in (3+2) Cycloaddition Reactions

The title heterocyclic alcohol readily generates a sulfur-substituted allylic cation upon simple treatment with a protic acid, thus facilitating a synthetically useful stepwise (3+2) cycloaddition reaction pathway with a range of conjugated-olefin-type substrates. The introduction of an allyl fragment in this way provided rapid access to a variety of cyclopentanoid scaffolds. The cyclic nature of the cation precursor alcohol was shown to be instrumental for efficient cycloaddition reactions to take place, thus indicating an attractive strategy for controlling the reactivity of heteroatom-substituted allyl cations. The formal cycloaddition reaction is highly regio- and stereoselective and was also used for a short total synthesis of the natural product cuparene in racemic form through a cycloaddition-hydrodesulfurization sequence.

Application of (4+3) cycloaddition strategies in the synthesis of natural products

This review summarizes the applications of (4+3) cycloadditions, both classical and formal, in the syntheses of natural products in the last two decades.

Exploration of fundamental and synthetic aspects of the intramolecular 4 + 3 cycloaddition reaction

In this Account, a summary of our work in the exploration and development of intramolecular 4 + 3 cycloaddition reactions between dienes and allylic cations is presented. Alkoxyallylic sulfones are useful precursors for the generation of allylic cations which are good dienophiles. Such substrates allowed a number of important pieces of data concerning the cycloaddition to be obtained. The evolution of the work has involved pursuing other methods for allylic cation generation, an investigation of stereochemical variables and applications, including the total syntheses of aphanamol I, widdrol, and (+)-dactylol.