Rapid, highly diastereoselective addition of dialkylzinc reagents to atropisomeric 2-formyl arylamides

We have observed that dialkylzinc reagents add to atropisomeric 2-formyl arylamides many times faster than they react with other substituted benzaldehyde derivatives. Additionally, with diethylzinc the products were formed with very high diastereoselectivity, affording the syn product (d.r. greater than 95:5), except in one case where epimerization of the product is rapid. In contrast, Grignard and trialkylaluminum reagents afforded the anti diastereomers, with diminished stereoselectivity and formation of reduction products.