Stereoselective Synthesis of Z-Styryl Sulfides from Nucleophilic Addition of Arylacetylenes and Benzyl Thiols.

The stereoselective synthesis of Z-anti-Markovnikov styryl sulfides via an anionic thiolate-alkyne addition reaction was achieved when the terminal alkynes and benzyl mercaptans were reacted using tBuOLi (0.5 equiv) in EtOH under ambient conditions. Exclusive stereoselectivity (ca. 100%) was achieved by stereoelectronic control via anti-periplanar and anti-Markovnikov addition of benzylthiolates to phenylacetylenes. Solvolysis of lithium thiolate ion pairs in ethanol significantly suppresses the competing formation of the E-isomer. A remarkable enhancement of the Z-selectivity under a longer reaction time was observed.

Activation of C-Br Bond of CBr4 and CBrCl3 Using 9-Mesityl-10-methylacridinium Perchlorate Photocatalyst.

Herein, we report the activation of the C-Br bond of CBrX3 (X = Cl, Br) using 9-mesityl-10-methylacridinium perchlorate as a visible-light (12W blue LED, 450-455 nm) photocatalyst for the synthesis of gem-dihaloenones from terminal alkynes. An electron transfer from CBrX3 to Mes-Acr-MeClO4 led to the formation of •+CBrX3 which subsequently resulted in the intermediate +CX3. Next, C-C cross-coupling of +CX3 with terminal alkynes was the key path to obtain the gem-dihaloenones. Radical trapping experiments with TEMPO, BHT, and Stern-Volmer quenching studies helped to understand that the reaction proceeded via the SET mechanism.