The synthesis of 3-spirooxindole derivatives. IX. The reactions of 2-hydroxytryptamine with hemiacetals.

The condensation of 2-hydroxytryptamine hydrochloride (IX) with the hemiacetals such as tetrahydropyran-2-ol (X) and morroniside (III), a member of the iridoids, was investigated. A condensation of IX with X was carried out by standing a solution of IX, X, and sodium acetate in the molar ratio of 1 : 1 : 2 in an aqueous ethanol at room temperature or at reflux for 42 hr to give the amino-alcohol (XI) in 85% yield, which was further characterized as two isomeric diacetyl derivatives (XIIa, XIIb). A condensation of IX with morroniside (III) was conducted under a similar condition only by heating a solution of the components at reflux for 42 hr to give the lactams (XIVa, b), which seemed to have been generated through the processes of the Mannich type of condensation like the preliminary work, followed by elimination of methanol. Attempts to prevent the lactam formation and to isolate the Mannich base were unsuccessful in the latter case, but the condensations of 2-hydroxytryptamine with hemiacetals were proved to have smoothly proceeded to afford the mannich bases in high yields.