Chalcogenide‐Lewis Acid Mediated Reactions of Electron‐Deficient Alkynes with Aldehydes

Abstract

Reactions of but-3-yn-2-one (2) with aldehydes 1 in the presence of a Lewis acid and dimethyl sulfide (3 a) predominantly gave (E)-alpha-(halomethylene)aldols 4-5 in high yields, while reactions of methyl propiolate (6 a) mainly afforded (Z)-3-halogeno-2-(hydroxymethyl)acrylates 7-8 in low to moderate yields. A reaction of dimethyl acetylenedicarboxylate (10) with 1 a in the presence of TiCl(4) and 1,1,3,3-tetramethylthiourea (3 c) produced maleate (E)-11 (40 %) and butenolide 12 (40 %). When a reaction of 6 a with 1 a was carried out in the presence of TiBr(4) and 3 a (0.2 equiv) at -20 degrees C for 60 h, 3-(methylthio)-2-(hydroxyalkyl)acrylate 9 a was obtained in an 8 % yield. Experiments were conducted in order to elucidate the formation mechanism of 9 a, and it was made clear that 9 a was formed via the processes of the Michael addition of sulfide 3 a to alkynoate 6 a and an aldol reaction with 1 a and demethylation.

Product Class 6: Oxonium Salts

“…[105] Vinyl sulfides have been used as masked carbonyl compounds. [106] 2-Ethynyl-3-phenyloxirane (12, R 1 = Ph); Typical Procedure: [102] To a stirred mixture of the hydroxy sulfide 11 (100 mg, 0.394 mmol) in CH 2 Cl 2 (8 mL) was added Me 3 OBF 4 (66 mg, 0.435 mmol). The mixture was kept at rt for 8 h, before a soln of 7% aq NaOH (5 mL) was added, and the resulting mixture was stirred for 20 min.…”

TiCl4-promoted condensation of methyl acetoacetate, isobutyraldehyde, and indole: a theoretical and experimental study

“…Although the use of Ti(IV) in Michael-type reactions has been known for almost forty years 12 with important applications in organic synthesis, [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] the number of mechanistic studies on such reactions is limited. [18][19][20][21][22][23][32][33][34][35][36][37][38][39] This study might contribute to elucidation of the trimolecular Scheme 1 TiCl 4 -promoted trimolecular condensation.…”

Asymmetric Tandem Michael‐Aldol Reactions between 3‐Cinnamoyloxazolidine‐2‐thiones and Aldehydes

“…[1] This reaction proceeded quickly, so the main defect of the Morita-Baylis-Hillman reaction [2] -its very slow reaction rate-was alleviated, so our reaction can be utilized as an alternative to the MoritaBaylis-Hillman reaction. During the course of our study we found that a chalcogenide caused the intramolecular Michael addition in the presence of a Lewis acid [3] and that a thioketone [4] or a thioamide [5] group worked as a catalyst. On the other hand, it is well known that N-unsubstituted thioamides undergo Michael additions with a,b-unsaturated carbonyl compounds.…”