Ketone Synthesis under Neutral Conditions. Cu(I) Diphenylphosphinate-Mediated, Palladium-Catalyzed Coupling of Thiol Esters and Organostannanes

Abstract

[reaction: see text] A versatile approach to ketone synthesis is described. The reaction relies on the palladium-catalyzed, copper diphenylphosphinate-mediated coupling of thiol esters with organostannanes under neutral reaction conditions. This reaction complements the previously described coupling of thiol esters with boronic acids that used dual thiophilic-borophilic activation methodology.

Organic Synthesis with Bimetallic Systems

“…The role of the Ag additive is assumed to be the removal of the chloride ligand from the complex, thereby freeing a coordination site and forming a more reactive cationic Rh center. Similar 6 and In(OTf) 3 and discussed a detailed analysis of the regioselectivity of the cyclization. Scheme 1.…”

“…These reaction activators most probably facilitate transmetalation of the organic group from the stannane to the palladium center through the formation of more reactive organometallic species such as vinylcopper, as shown in Scheme 1.4. Liebeskind and co-workers [6] have recently reported the Stille-type coupling reaction between thiol esters and organostannanes (Scheme 1.5) The reaction proceeded in the presence of a combination of Pd 2 (dba) 3 /(2-furyl) 3 P as catalyst and CuOP(O)Ph 2 as an activator. The role of the Cu additive is activation of the acylpalladium thiolate intermediate to facilitate transmetalation of the aryl group from the stannane to the palladium atom.…”

“…The catalyst was prepared in situ from [RhCl(dppb)] 2 and AgSbF 6 . The role of the Ag additive was to generate an active cationic Rh species.…”

“…A bimetallic catalyst comprising CpRu(COD)Cl and SnCl 4 · 5 H 2 O was found to be the optimal catalyst system for this transformation. When LiBr was used as a nucleophilic agent, (Z)-vinyl bromides were obtained as the major products in the presence of [CpRu(MeCN) 3 ]PF 6 and SnBr 4 catalysts (Scheme 1.90) [116]. The high Z-selectivity in forming the adducts can be rationalized by invoking a mechanism in which the vinylruthenium intermediate is formed by cis-addition of a neutral Ru-Br species to the alkyne.…”

Enantioselective Synthesis of the (1S,5R)-Enantiomer of Litseaverticillols A and B

“…The chiral auxiliary of (E)-5 was substituted by an ethylthio group to give (E)-6 without any epimerization at the position to the carbonyl by using ''EtSCeCl 2 '' prepared by mixing EtSLi and CeCl 3 in a ratio of 1:1; this seems to be the first example, to our knowledge, of utilizing the ''RSCeCl 2 '' species for the preparation of thiol esters. In our previous synthesis of the (1R,5S)-isomer of 1 and 2, we employed EtSLi itself, 4,9) which resulted, although only occasionally, in a small degree of undesirable epimerization at theposition to give (E)-6 with a reduced 88% diastereomeric excess (de) in the worst case when we failed to keep the reaction temperature below À15 C. Diastereomerically pure thiol ester (E)-6 was then subjected to the Liebeskind-Srogl esterification reaction 10) at 80 C under microwave irradiation to give an almost quantitative yield (96%) of (E)-7.…”