Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones.

A wide range of -(ethoxycarbonylmethyl)enaminones, prepared by the Eschenmoser sulfide contraction between -(ethoxycarbonylmethyl)pyrrolidine-2-thione and various bromomethyl aryl and heteroaryl ketones, underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1-pyrrolizine-5-carboxylates within minutes upon microwave heating in xylene at 150 °C. Instead of functioning as a nucleophile, the enaminone acted as an electrophile at its carbonyl group during the cyclization. Yields of the bicyclic products were generally above 75%.

1-(2-Hy-droxy-4,5-dimeth-oxy-phen-yl)ethanone.

The mol-ecular structure of the title compound, C10H12O4, contains an intra-molecular hydrogen bond between the phenol and acetyl substituents. In the crystal, C-H⋯π inter-actions act between the mol-ecules in a cyclic manner to stabilize stacks of mol-ecules along the b axis. Several C-H⋯O inter-actions are present between the stacks.