Enantiospecific Synthesis of the trans-9-carbazoles

Article abstract of DOI:10.1021/jo00209a002

The compounds in the title, (R,R)- and (S,S)-2, are isomers of the cis-dimethyl compound 1, which is in human trials as an antipsychotic.They were made starting with chiral alanine esters (6) and the 2-bromopropionic esters made from the alanines of opposite chirality (5) and proceeding by cyclization of the ethoxycarbonyl-protected iminodipropionic acids 9, via anhydride 10, with 3-(9-carbazolyl)propylamine and subsequent BH3 reduction of the imides 12 followed by hydrolytic removal of the COOEt.Selection of the reagents necessary to minimize racemization <α>_D ²⁰ values at each condensation stage and the 1H and 13C NMR absorption data required for structure proof of 2 are given; a ring inversion rate of 5200 s^-1 is calculated based on low and ambient temperature 13C NMR data.