Stereochemistry and Mechanistic Study of Intramolecular Pd^II‐Catalyzed Oxypalladation and 1,3‐Chirality‐Transfer Reactions

Abstract

Pd(II)-catalyzed cyclizations of chiral epsilon-, zeta-, and eta-hydroxy-alpha,beta-unsaturated alcohols are described. The reactions took place stereospecifically to give chiral 2,5-disubstituted tetrahydrofurans, 2,6-disubstituted tetrahydropyrans, and 2,7-disubstituted oxepanes, respectively. The chirality of the carbon center of the chiral allylic alcohol is transferred stereospecifically to the carbon center of the newly generated oxacyclic ring. A plausible reaction mechanism involves 1) chiral-allylic-alcohol-induced syn facioselective formation of a Pd pi-complex, 2) syn oxypalladation, and 3) syn elimination of PdCl(OH), which provide a rational account for the stereochemical results.

Palladium(II)-catalyzed dicarboxymethylation of chiral allylic alcohols: chirality transfer affording optically active diesters containing three contiguous chiral centers

“…The e.e. of 2 was established to be 69.7% as determined by 1 H NMR in the presence of lanthanide shift reagent Eu(hcf) 3 , thus the reaction proceeded in 98% diastereoselectivity (Table 1) The product distribution and relative stereochemistries are consistent with the proposed mechanism (Scheme 2), similar to the mechanism proposed by Uenishi 13 for an intramolecular palladium(II)-catalyzed oxypalladation and 1,3-chirality transfer. Thus, the hydroxyl group directs the palladium to the face that produces the most stable π-complex 4, which in turn depends on the absolute configuration of the starting allylic alcohol 1.…”

“…Thus, the hydroxyl group directs the palladium to the face that produces the most stable π-complex 4, which in turn depends on the absolute configuration of the starting allylic alcohol 1. 4,[10][11][12][13] Addition of carbon monoxide to complex 4 followed by insertion of methanol yields the olefin-carbomethoxypalladium intermediate 5, which undergoes insertion of the carbomethoxy group to produce the σ-complex 6. 14,19 Adduct 6 then either undergoes further syn addition of CO to give desired 2, or loses a proton and eliminates palladium yielding an enol which tautomerizes to ketone 3.…”

“…[10][11][12][13] We presently wish to report the extension of chirality transfer from chiral allylic alcohols utilizing Stille's palladium-catalyzed olefin dicarbonylation reaction. 14 In this context is it noteworthy that a number of groups have explored the use of chiral catalysts with the Stille bis-alkoxycarbonylation for the asymmetric construction of chiral bis-esters.…”

Synthesis of (+)-Muconin via Diastereoselective Oxypalladation

“…Uenishi and coworkers proposed the mechanism of the catalytic cycle of 1,3-chirality transfer in intramolecular oxypalladation . By referring to Uenishi’s proposal, we wish to suggest a mechanism of catalytic cycle in this reaction.…”

Synthesis of Spiro C-Arylglycoriboside via Pd(II)-Catalyzed Spirocyclization

“…A plausible mechanism of Pd(II)-catalyzed spirocyclization is illustrated in Scheme 5. 11 The hemiketal 2¢ exists in equilibrium with hemiketal A, B and keto alcohol. Pd-p complex is formed by coordination of PdCl 2 with allylic ether at one p-face of the olefin with the assistance of the adjacent hydroxy group.…”