The Synthesis of Octahydro‐7‐phenylpyrazino[2,1‐b][3]benzazepines

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Abstract
Octahydro‐7‐phenylpyrazino[2,1‐b][3]benzazepine (1a) was prepared from 1‐methyl‐3‐phenylmethylpiperazine5aby reaction with styrene oxide followed by sulfuric acid cyclization of the resulting alcohol6a. The diastereomeric mixture1awas further separated into the diastereomers1a′and1a″. Similarly 1‐methyl‐3‐(3‐chloro‐4‐methoxyphenyl)piperazine was reacted with styrene oxide to yield6cwhich on cyclization with 1.5 equivalents of sulfuric acid in trifluoroacetic acid gave a 3:7 mixture of phenolic,1d, and methoxy,1c, octa‐hydropyrazino[2,1‐b][3]benzazepines. The reaction of the 2,5‐piperazinedione4cwith sodium acetoxyborohydride gave a 49% yield of the 2‐piperazinone7which was similarly carried on to the corresponding 1(2H)‐oxohexahydropyrazino[2,1‐b][3]benzazepine9.