Chalcogenide-TiCl4-mediated reactions of S-ethyl thioacrylate with aldehydes

The reaction of p-nitrobenzaldehyde (1a) with S-ethyl thioacrylate (2) catalyzed by chalcogenide-TiCl4 gave a mixture of Baylis–Hillman adduct 4a and syn- and anti-2-(chloromethyl)-3-hydroxy-3-(p-nitrophenyl)propanethioates 5a in the ratio of 4:syn-5:anti-5=5:65:30. The crude product obtained from the reaction of p-trifluoromethyl derivative 1b with 2 was treated with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in toluene to give 4 in 71% overall yield, while treatment of the crude product with Ti(O-i-Pr)4 afforded isopropyl 2-(α-hydroxy-p-trifluoromethylbenzyl)acrylate 6 (49%), S-ethyl 2-(ethylthiomethyl)-3-hydroxy-3-(p-trifluoromethylphenyl)thiopropyonate 7 (2%) and S-ethyl 2-(chloromethyl)-3-(p-trifluoromethylphenyl)thioacrylate 8 (15%). Reactions of 2 with other various aldehydes followed by the treatment with DBU or Ti(O-i-Pr)4 gave the thioacrylates 4 and isopropyl acrylates 6, respectively, in fair to good yields. The formation mechanism for 2-(chloromethyl)propanethioate 5 is discussed.