Regioselective Alkenylation of Five-Membered Heteroarenes via a Dual 1,3-Sulfur Rearrangement

Abstract

Herein, we report a protocol for the stereoselective C–H alkenylation of five-membered heteroarenes including pyrroles (containing free NH pyrrole), thiophenes, and furans with 1,3-dithiane derivatives through dual 1,3-sulfur rearrangements. The site-selective and regioselective alkenylation of the five-membered heteroarenes proceeded in good yields via vinyl thionium ions to produce C2 or C5 Heck-type products, respectively.

Indium-catalyzed inter- and intramolecular dithianyl–alkyne metathesis reactions

“…11 Over the past few years, our group has also contributed to this field by developing a 1,3-sulfur rearrangement strategy of dithianes for the stereoselective synthesis of alkenyl products. 12–14 These transformations demonstrated the high potential of in situ generated thionium ions from 1,3-dithianes in carbon–carbon bond formation reactions (Scheme 1b). Based on these findings, we herein developed a novel metathesis reaction between 1,3-dithiane and alkyne, and the newly formed thionium ion from 1,3-dithiane could undergo [2+2] cycloaddition with alkyne either inter- or intramolecularly (Scheme 1c).…”

Stereoselective Synthesis of Highly Substituted 1,3-Dienes through Dual 1,3-Sulfur Rearrangement of Dithianes with Alkynylsilanes

“…Based on the control experiments and our previous studies, we proposed the mechanism shown in Scheme c. The Lewis acid accelerates the formation of vinyl thionium ion A via the ring opening of dithianes, whereas intermolecular nucleophilic addition of the newly formed thionium ion species generates the corresponding 1,4-enyne B .…”

“…However, the use of alkynes as nucleophiles and the introduction of the CC bond may have changed this tendency. Therefore, the ring opening of the dithianyl moiety and Lewis acid-based addition with the CC vs CC routes present the regioselective challenge (Scheme b). , We hypothesized that the highly reactive triple bond of alkyne would be competent to trigger the first sulfur-alkyne addition, followed by the sequential 1,3-sulfur migrations to result in the dithianyl-substituted 1,3-dienes. We herein present the stereoselective synthesis of highly substituted 1,3-dienes through the dual 1,3-sulfur migration of 1,3-dithiane derivatives with widely available alkynylsilanes (Scheme b).…”

“…Dithiane compounds are a class of powerful acyl equivalents in organic synthesis . Our group has developed a dual 1,3-sulfur rearrangement strategy of dithianes for the stereoselective synthesis of alkenyl products . Alkenyl dithianes have been recognized as excellent alkenyl precursors to engage various nucleophilic groups in alkenylation reactions.…”