Synthesis and reactivity of lithiated γ-functionalised ketene dithioacetals. Generation of a flexible β-lithioacrylate equivalent

Acylvinyl and Vinylogous Synthons

“…Thus, the anion 371 of 1,1,3-tris(phenylthio)propene ( 370 ), which can be considered as a β-lithioacrylic acid equivalent, reacts with electrophiles to give the γ-substituted adducts. Hydrolysis of the intact dithioacetal moiety serves to release the latent carboxylate function and elimination of thiophenol generates the corresponding β-substituted acrylic acids. , In the case of the reaction with aldehydes or ketones, cyclization and elimination of thiophenol generates the corresponding butenolides, as shown in Scheme outlining the preparation of butenolide 373 , which has been used as a precursor of the pheromone (±)-eldanolide . Even chemically similar 1,1,3,3-tetraalkylthio-substituted propenes such as 2-(1,3-dithian-2-ylidenemethyl)-1,3-dithiane ( 374 ) can be lithiated and used now as an equivalent of the β-hydroxy-β-lithioacrylic acid for the synthesis of (±)-dihydrokawain ( 377 ) following the route outlined in Scheme …”

“…192,193 In the case of the reaction with aldehydes or ketones, cyclization and elimination of thiophenol generates the corresponding butenolides, as shown in Scheme 84 outlining the preparation of butenolide 373, which has been used as a precursor of the pheromone (()-eldanolide. 193 Even chemically similar 1,1,3,3-tetraalkylthio-substituted propenes such as 2-(1,3-dithian-2-ylidenemethyl)-1,3-dithiane (374) can be lithiated and used now as an equivalent of the β-hydroxy-β-lithioacrylic acid for the synthesis of (()-dihydrokawain (377) following the route outlined in Scheme 85. 194 The lithio derivative 381 of 2-diethylamino-4phenylthiobut-2-enenitrile (380) is also a practical β-lithioacrylic acid equivalent.…”