Preparation and Diastereoselective Birch Reduction−Alkylation of Chiral 3,4-Dihydro-1(2H)-isoquinolinones. Enantiospecific Syntheses and Opioid Receptor Affinities of Several Hydro-2,3- dimethyl-1H-7,12a-methanobenzo[6,7]cycloocta[1,2-c]pyridine-9-ols

Abstract

Synthetic procedures have been developed to provide 2,3-disubstituted-3,4-dihydro-1(2H)-isoquinolinones 6, 10, and 15 from (1R,2S)-ephedrine, (1R,2R)-pseudoephedrine, and l-phenylalanine. Birch reduction of 6 and 10 gave enantiomerically related lactam enolates that were alkylated with methyl iodide, allyl bromide, benzyl bromide, p-benzyloxybenzyl bromide, and p-methoxybenzyl bromide to give 7a−7e, 11a, and 11b with diastereoselectivities > 20:1. Birch reduction−methylation of 15 gave 19 with a diastereoselectivity of >35:1. Selective reduction of the disubstituted double bond in 19 with diimide and cleavage of the tert-butyldimethylsilyl ether gave 20b, from which iodoetherification under thermodynamic control gave the iodopyran 21a; iodoetherification of 20b under kinetic control gave the iodotetrahydrofuran 22. Enantiospecific syntheses of analogues of 24 (Schultz, A. G.; Kirincich, S. J.; Rahm, R. Tetrahedron Lett. 1995, 36, 4551−4554) have been developed. Tetracycle 24 is isomeric with the potent analgesic agent levorphanol, but the bridging of the hydroisoquinoline ring by the hydroxybenzyl unit in 24 is at C(7, isoquinoline numbering) and C(8a) rather than at C(1) and C(4a) as in levorphanol. The key step in the transformation of 7d and 7e to tetracyclic phenolic amines (−)-26 and (+)-28 is the Grewe-type cyclization of 7d to 25b and 7e to 25c. Ki values for the inhibition of binding to the μ-, δ-, and κ-opioid receptors by (−)-26, (+)-26, (+)-28, (−)-28, and (+)-32 are reported.