上海科技大学知识管理系统

Axially chiral compounds represent an important class of chiral molecules. In this regard, many methods have been developed to access these compounds. However, efficient methods for the synthesis of axially chiral styrenes are limited to date, mainly due to their relative instability compared to axially chiral biaryl compounds. Iridium-catalyzed asymmetric ally lic substitutions have evolved as a powerful tool in constructing C-C or C -X bonds at the allylic position. We developed an efficient sequential strategy to access a series of axially chiral styrenes by iridium-catalyzed allylic substitution and central-to-axial chirality transfer via olefin isomerization. With the iridium complex derived from [Ir(cod)Cl](2) and Alexakis ligand L1 as catalyst, and beta-naphthol as nucleophiles, a broad range of axially chiral styrenes were obtained with moderate to excellent yields (28%similar to 97% yields) and enantioselectivity (59%similar to 98% ee). A general procedure for the asymmetric allylation of beta-naphthol is described as the following: A flame-dried Schlenk tube was cooled to mom temperature and filled with argon. To this flask were added [Ir(cod)Cl](2) (2.6 mg. 0.004 mmol, 2 mol%), (S,S,S-a)-L1 (4.8 mg, 0.008 mmol, 4 mol%), freshly distilled tetrahydrofuran (THF, 0.5 mL) and propyltunine (0.5 mL). The mixture was stirred at 50 degrees C for 30 min and then the low-boiling solvents were removed in vacuo to give a pale yellow solid. The solid was stirred at 50 degrees C again under vacuum until it became a powder. After that, beta-naphthol 1 (0.22 mmol, 1.1 equiv.), allyl carbonate 2 (0.2 mmol, 1.0 equiv.), 1,4-diazobicyclo(2.2.2)octane (DABCO) (67.3 mg, 0.6 mmol, 3.0 equiv.) and freshly distilled Et2O (2.0 mL) were added to this flask under argon atmosphere. The reaction mixture was stirred at 20 degrees C until the starting material was consumed (monitored by thin layer chromatography, TLC). The crude reaction mixture was diluted with water (5 mL), and extracted with dichloromethane (DCM, 5 mL X 3). The organic layers were collected, dried over Na2SO4 and then concentrated in vacuo to afford the crude product. The residue was purified by preparative TLC to aftbrd the product.