Palladium-Catalyzed Carbocyclization/Silastannylation and Distannylation of Bis(allenes)

Abstract

-046Palladium-Catalyzed Carbocyclization/Silastannylation and Distannylation of Bis(allenes).-The first Pd-catalyzed carbocyclization of bis(allenes) leading to five-membered rings via silastannylation and distannylation, respectively, is presented. A striking reversal of stereochemistry is observed changing from silastannylation to distannylation.

Reaction mechanism of palladium‐catalyzed silastannation of allenes by density functional theory

“…For the bisallenes in which there are two allene functional groups, both the silyl and stannyl groups add to the internal sp-carbon atom. 21 It seems that the internal sp-carbon atom is favored over the terminal sp 2 -carbon atom for silyl and stannyl additions. The reaction mechanism of silastannation of allenes was proposed to proceed via oxidative addition, allene insertion into PdÀ ÀSi bond to provide the p-allylpalladium species, and finally reductive elimination.…”

Cyclization reactions of bis(allenes) for the synthesis of polycarbo(hetero)cycles

“…Bis(allenes) 1 reacted with (trimethylsilyl)tributylstannane in 25 the presence of a catalytic amount of Pd(PPh 3 ) 4 (5 mol%) in refluxing THF, affording trans-fused cyclized compounds 142 in good yields. 46 By contrast, when the same allenes 1 were treated with Bu 3 SnSnBu 3 , the Pd(0)-catalyzed cyclization process took place smoothly to afford cis-fused distannanes 30 143 (Scheme 52). Analogously, similar Pd-catalyzed cyclizations of 1,5-bis(allenes) with germylstannanes have been accomplished under the conditions described above.…”

Development of Useful Reactions Involving Tandem Cyclizations Based on the Novel Reactivities of Allenic Compounds

“…Recently, cyclizations of bisallenes on treatment with silylstannane and palladium(0) were independently reported by two research groups. 73,74) Palladium(II)-catalyzed oxidative cyclization of allene-substituted alkenes and palladium(0)-catalyzed cyclization of allenes bearing an allyl ester moiety were reported by Bäckvall. 75,76) Oh and co-workers reported cyclization of allenynes in the presence of a palladium catalyst and organic acid.…”