Enantioselective iodolactonization to prepare ε-lactone rings using hypervalent iodine.

Despite the rapid growth of enantioselective halolactonization reactions in recent years, most are effective only when forming smaller (6,5,4-membered) rings. Seven-membered ε-lactones, are rarely formed with high selectivity, and never without conformational bias. We describe the first highly enantioselective 7-exo-trig iodolactonizations of conformationally unbiased ε-unsaturated carboxylic acids, effected by an unusual combination of a bifunctional BAM catalyst, I2, and I(iii) reagent (PhI(OAc)2:PIDA).

Role of Hydrogen-Bonding Acceptors in Organo-Enamine Catalysis.

A hydrogen bond acceptor plays an important role in the catalytic cycle of organo-enamine catalysis. It can effectively influence the rate of reaction through hydrogen bonding interaction with enammonium (N-protonated enamine intermediate). Our findings are supported by both kinetic experiments and quantum chemical calculations.