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

Abstract

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.

An Intramolecular Cycloaddition Approach to the Kauranoid Family of Diterpene Metabolites

“…Finally, inspired by recent research results from our group involving allyl cation-type cycloadditions derived from dihydrodithiin-substituted alcohols, , we also briefly explored this heterocycle type. One advantage of this cycloaddition-mediating sulfur heterocycle is the fact that it can be removed via hydrodesulfurization, resulting in the product of a formal (4 + 3) cycloaddition of a naked allyl cation.…”

“…These minor side products appear to correspond to the product of a competitive allyl cation (3 + 2) cycloaddition. Indeed, in previous studies on this heterocycle, we found that (3 + 2) cycloaddition pathways can also occur. , …”

Stereoselective and Modular Assembly Method for Heterocycle‐Fused Daucane Sesquiterpenoids

“…[17] In this way,2 -methyl thiophene was found to perform almost equally well ( Table 2, 7). Benzothiophene also gave ar easonable yield of the expected daucanoid 8, albeit with al ower diastereoselectivity.I nl ight of more recent promisingr esearch results obtained with dihydrodithiinsincationic cycloadditions, [18] we were eager to test this unusualh eterocycle in this scheme. [19] Remarkably, this sulfur-heterocycle gave ah ighly efficient cycloaddition ( 2,9), that was however selective for ad ifferentr ing fusion isomer,astriking mechanistic discrepancy from the previous examples that was also confirmedb yX -ray structures of analogous compounds (vide infra, Figure 1).…”