Enantioselective Rh-Catalyzed Domino Transformations of Alkynylcyclohexadienones with Organoboron Reagents

Abstract

A new enantioselective rhodium-catalyzed domino reaction is described that gives access to fused heterocycles by desymmetrization of alkyne-tethered cyclohexadienones. Two new C-C bonds and two stereocenters are formed in one step with good enantioselectivity. In contrast to prior reports, it was found that a vinylidene is not involved in the product formation but that syn-addition of the rhodium-aryl species onto the alkyne takes place.

Phosphazene-catalyzed desymmetrization of cyclohexadienones by dithiane addition

“…The Sasai and Enders groups used a phosphinothiourea to enable a Rauhut–Currier reaction to form bicyclic enones [16]. The Tian and Lin group used alkyne-tethered cyclohexadienones in an arylrhodation/conjugate addition sequence that enantioselectively delivered oxabicyclo[4.3.0]nonanes [17]; the Lautens and Lan groups have also contributed to the further development of this reaction [18–19]. The Rovis group employed cyclohexadienone hydroperoxides in a chiral phosphoric acid-catalyzed [1,2]/[1,4]-addition cascade [20].…”

Asymmetric transformations of achiral 2,5-cyclohexadienones

“…26 Subjecting substrates 55 and aryl boronic acids to catalytic [Rh(coe) 2 Cl] 2 in the presence of chiral diene ligand 57 provided bicyclic enones 56 in moderate yields and with good stereocontrol (Scheme 12). The authors found that the stereoselectivity of the reaction was generally insensitive to both the nature of the aryl boronic acid and to variations of the alkyne tether (products 58 – 61 ).…”

Asymmetric Induction at Remote Quaternary Centers of Cyclohexadienones by Rhodium‐Catalyzed Conjugate Hydrosilylation

“…Thesubsequent treatment of 3aunder acidic conditions gave the desired cyclohexenone 4a with an all-carbon quaternary center at the g-position in 52 %y ield (Table 1, entry 1). Next, we examined the effect of the substituents on [Rh(Phebox-R)] (1;T able 1, entries [6][7][8]. Next, we screened aseries of hydrosilanes as reductants.Ofthe alkoxyhydrosilanes tested, the reaction with trimethoxysilane gave the best result (90 % yield, e.r.…”