Palladium catalyzed thiocarbonylation and related reactions of functionally substituted alkenes and alkynes, allenes, and enynes.

Abstract

A systematic investigation has been carried out on the palladium-catalyzed thiocarbonylation and related reactions of unsaturated substrates such as propargylic and allylic alcohols, 1,2- and 1,3-dienes, and conjugated enynes with thiols and carbon monoxide. It has been first demonstrated that the reaction of allylic alcohols with thiols and CO in the presence of catalytic quantities of Pd(OAc) 2 (3 mol%), triphenylphosphine (12 mol%), and p-TsOH (5 mol%) leads to a novel reaction, namely thiocarbonylation, to afford beta,gamma-usaturated thiol esters in good to excellent yields. Other catalyst systems such as Pd 2(dba)3·CHCl3/PPh3/p-TsOH, Pd(PPh 3)4/p-TsOH, and Pd(OAC)2/dppb/ p-TsOH are also effective for this transformation. The thiocarbonylation reaction is believed to proceed via a eta3-allylpalladium intermediate. The reaction occurs in a highly regioselective manner, at the least hindered allylic terminal carbon of the substrate, to give the products. The new carbonylation procedure was readily applied to a variety of allylic alcohols, and to both aromatic and aliphatic thiols. Palladium (0) as well as palladium (II) complexes with added phosphine ligands catalyze the thiocarbonylation of propargylic compounds. Depending on the reaction conditions employed, the reaction can afford mono- and di-thioesters or beta-thio-substituted gamma-lactones as the principal products in good yields, respectively. Thus, in the presence of 3 mol% of Pd(OAC)2, 5 mol% of p-TsOH, and 12 mol% of PPh3, propargylic alcohols react with thiols in THF under 400 psi of carbon monoxide at 100°C to give monothioesters in excellent yields. beta-Thio-alpha,beta-unsaturated-gamma-lactones can be prepared in high yields by the thiolactonization of propargylic alcohols using Pd(PPh3)4 as the catalyst and DME as the solvent. Propargylic mesylates undergo dithiocarbonylation when they are treated with catalytic amounts of Pd(PPh3)4. This reaction exclusively gives dithioesters under milder conditions (90°C, 400 psi). A series of mono- and di-substituted allenes undergo direct thiocarbonylation with thiols and carbon monoxide to form the corresponding unsaturated thioesters in 73--94% isolated yields. This reaction requires catalytic quantities of Pd(OAC)2 (3 mol%) and triphenylphosphine (12 mol%) in THF under an atmosphere of CO (400 psi) at 100°C for 48 h. The reaction is believed to proceed via pi-allylpalladium complex. The reaction exhibits high regioselectivity, in which the thiophenyl group adds to the less substituted double bond of allenes. (Abstract shortened by UMI.)