Novel Stereoselective Syntheses of the Fused Benzazepine Dopamine D₁ Antagonist (6a<i>S</i>,13b<i>R</i>)-11-Chloro-6,6a,7,8,9,13b-hexahydro-7-methyl-5<i>H</i>- benzo[<i>d</i>]naphth[2,1-<i>b</i>]azepin-12-ol (Sch 39166): 1. Aziridinium Salt Based Syntheses

Abstract

Several novel enantioselective syntheses of the dopamine D1 antagonist (6aS,13bR)-11-chloro-6,6a,7,8,9,13b-hexahydro-7-methyl-5H-benzo[d]naphth[2,1-b]azepin-12-ol (2) are described in which the key intermediate was 1-(2,2-dimethoxyethyl)-1-methyl-1a,2,3,7b-tetrahydro-1H-naphth[1,2-b]aziridinium salt (20). The latter species was prepared either from 1-(2,2-dimethoxyethyl)-1a,2,3,7b-tetrahydro-1H-naphth[1,2-b]azirine (18) by methylation or from the tertiary amino alcohols 1-[(2,2-dimethoxyethyl)methylamino]-1,2,3,4-tetrahydro-2-naphthalenol (23) or 2-[(2,2-dimethoxyethyl)methylamino]-1,2,3,4-tetrahydro-1-naphthalenol (24) by tosylation and in situ ring closure. Regioselective trapping of 20 with Grignard reagent (4-chloro-3-methoxyphenyl)magnesium bromide (10) then afforded the trans amine 1-(4-chloro-3-methoxyphenyl)-N-(2,2-dimethoxyethyl)-1,2,3,4-tetrahydro-N-methyl-2-naphthalenamine (22), which was cyclized to give 11-chloro-6,6a,7,8,9,13b-hexahydro-7-methyl-12-methoxy-5H-benzo[d]naphth[2,1-b]azepine (9), a known precursor of 2. Several enantioselective syntheses, including a Jacobsen epoxidation route, a de novo synthesis from l-homophenylalanine, and a classical salt resolution sequence, were developed for the preparation of the key intermediates in chiral form.