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

The reaction of p-nitrobenzaldehyde (la) with S-ethyl thioacrylate (2) cata lyzed by chalcogenide-TiCl4 gave a mixture of Baylis-Hillman adduct 4a and syn- and anti-2-(chloromethyl)-3-hydroxy-3-(p-nitrophenyl)propanethioates 5 a in the ratio of 4:syn-5:anti-5 = 5:65:30. The crude product obtained from the reaction of p-trifluoromethyl derivative Ib 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 iso propyl 2-(alpha-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), gave the thioacrylates 4 and isopropyl acrylates 6 , respectively, in fair to good yields. The formation mechanism for 2-(chlo romethyl)propanethioate 5 is discussed. (C) 2000 Elsevier Science S.A. All rights reserved.