Tunable arylative cyclization of 1,6-enynes triggered by rhodium(III)-catalyzed C-H activation.

Two tunable arylative cyclizations of cyclohexadienone-containing 1,6-enynes are reported via rhodium(III)-catalyzed C-H activation of O-substituted N-hydroxybenzamides. The use of different O substituents, i.e. O-Piv and O-Me, on the directing group allows the formation of either tetracyclic isoquinolones through an Ⓝ-Michael addition process or hydrobenzofurans through a Ⓒ-Michael addition process. Mechanistic investigations of these two cascade reactions clearly indicated that the C-H bond cleavage process was involved in the turnover-limiting step. Furthermore, the cyclization products could be subjected to various transformations for elaborating the pharmaceutically and synthetically valuable potential. This is the first example of a rhodium(III)-catalyzed arylative cyclization reaction of 1,6-enynes, and the results extend the application realm of Cp*Rh(III)-catalyzed C-H activation cascade reactions.

Cu-catalyzed asymmetric borylative cyclization of cyclohexadienone-containing 1,6-enynes.

The first Cu-catalyzed asymmetric borylative cyclization of cyclohexadienone-containing 1,6-enynes is achieved through a tandem process: selective ß-borylation of propargylic ether and subsequent conjugate addition to cyclohexadienone. The reaction proceeds with excellent regioselectivity and enantioselectivity to afford an optically pure cis-hydrobenzofuran framework bearing alkenylboronate and enone substructures. Furthermore, the resulting bicyclic products could be converted to bridged and tricyclic ring structures. This method extends the realm of Cu-catalyzed asymmetric tandem reactions using bis(pinacolato)diboron (B2pin2).

Asymmetric synthesis of ß-substituted γ-lactams via rhodium/diene-catalyzed 1,4-additions: application to the synthesis of (R)-baclofen and (R)-rolipram.

An efficient rhodium/diene-catalyzed asymmetric addition of arylboronic acids to α,ß-unsaturated γ-lactams has been developed. The power of this methodology is further demonstrated by the concise synthesis of (R)-baclofen and (R)-rolipram.

C1-symmetric dicyclopentadienes as new chiral diene ligands for asymmetric rhodium-catalyzed arylation of N-tosylarylimines.

Monosubstituted C(1)-symmetric dicyclopentadienes as a new class of diene ligands have been developed for asymmetric arylation of N-tosylarylimines in excellent yields (98-99%) with high enantioselectivities (90-96%). The preparation of these diene ligands relied on an efficient lipase-catalyzed resolution as the key step.