Synthesis of chromans
A convergent three-step method provides 2-substituted chromans via Heck coupling of readily accessible allylic alcohols and 2-iodophenols, followed by reduction and Mitsunobu cyclization. The utility and generality of this method is demonstrated through the synthesis of a series of 2-aryl-, 2-heteroaryl- and 2-alkylchromans, as well as an azachroman derivative. A Noyori-catalyzed ketone reduction enables an asymmetric version.
R. K. Orr, L.-C. Campeau, H. R. Chobanian, H. M. McCabe Dunn, B. Pio, C. W. Plummer, A. Nolting, R. T. Ruck, Synthesis, 2017, 49, 657-666.
A bifunctional aminoboronic acid facilitates intramolecular aza- and oxa-Michael reactions of α,β-unsaturated carboxylic acids. The combination of an arylboronic acid with a chiral aminothiourea enables enantioselective conversions to afford the desired heterocycles in high yields and ee’s (up to 96% ee).
T. Azuma, A. Murata, Y. Kobayashi, T. Inokuma, Y. Takemoto, Org. Lett., 2014, 16, 4256-4259.