Asymmetric Dearomatization of the Furan Ring Promoted by Conjugate Organolithium Addition to (Menthyloxy)(3‐furyl)carbene Complexes of Chromium

Abstract

The sequential low-temperature addition reaction of an organolithium compound and methyl triflate to (menthyloxy)(3-furyl)carbene complexes of chromium and tungsten proceeded with excellent regioselectivity (1,4-addition) and diastereoselectivity (2,3-trans disposition of the nucleophile and electrophile groups) to afford new 2,3-disubstituted (2,3-dihydro-3-furyl)carbene complexes. In addition, a high degree of diastereofacial selectivity was achieved by employing alkenyllithium compounds. After detachment of both the metal fragment and the chiral auxiliary group, trisubstituted 2,3-dihydrofuran derivatives containing a quaternary stereogenic center at the C3 position were obtained. The characterization, including X-ray crystallography, of a novel type of stable four-membered chelate (eta(2)-alkene)tetracarbonylcarbene complex of chromium is also reported.

Enantioselective Annulation Reactions of Bisenolates Prepared Through Dearomatization Reactions of Aromatic and Heteroaromatic Diesters

“…Dearomatized furans [12] have been previously obtained by a decarboxylative Claisen rearrangement, [7b] [2,3]-Still-Wittig rearrangement, [13] aryl radical addition [14] and nucleophilic addition to carbene complexes of chromium, [15] among other methods. [16] Furan diester 7 (X = O) was prepared in iPrOH by the Fischer esterification of the corresponding diacid, which was obtained by regioselective deprotonation of 3-furoic acid at C-2 with BuLi followed by quenching with carbon dioxide.…”

Fischer-Type Group 6 Carbene Complexes in the Synthesis of Optically Active Molecules

“…Very interesting stereoselective dearomatization reactions have been achieved by Barluenga furylcarbene complexes 66 react with organolithium derivatives in a diastereoselective Michael-type reaction (Scheme (23)) [39]. Capture of the intermediate with methyl triflate and further transformations lead to the corresponding dihydrofurans 68 and 69 with high regio-, diastereo-and face selectivity.…”

Five‐Membered Heterocycles: Furan

“…Consecutive oxidative decomplexation and reductive cleavage of the chiral auxiliary provides 2,3-dihydrofuran 166, which contains a quaternary C3 center [136].…”