Pentazocine prepn - by reduction of the n-benzyl deriv with raney-cobalt

摘要

Process for prepn. of pentazocine (I) by reacting a cmpd. (III): with X.CH2.CH=C (where X is halogen) in the presence of an aliphatic ketone at -10 to +30 degrees C and reducing the cmpd. (II) formed with Raney Co and NH3. (I) is an analgesic and the process gives better yields (avoids use of Grignard reagents) than known processes. EXAMPLE A mixt. of 50 pts. (III) in 250 pts. dry acetone with 29.2 pts. 1-bromo-3-methyl-2-butene in 20 pts. acetone was stirred 72 hrs. and evapd. in vacuo to give 73.9 pts. (II) bromide m.pt. 163-6 degrees C (alpha-isomer). Ether was added to the mother liquors from the recrystallisation to give beta-isomer m.pt. 205-6.5 degrees C, 1.07 pts. (II), bromide (beta-isomer). 1.07 pts. beta isomer in 25 pts. ethanol and 0.250 pts. gaseous NH3 were reduced with 2.5 pts. Raney Co at normal temp. and pressure until 53 pts. H2 had been absorbed to give 0.620 pts. (I) (0.537 pts. after chromatographic purification). Reduction of the alpha-isomer also gave (I).