ChemInform Abstract: The Tandem Pauson‐Khand Reaction.

Abstract

Dedicated to Hans-Dieter Scharfon the occasion of his 65th birthday (28.X11.95)The conditions for the novel tandem Pauson-Khand reaction have been explored. The highly functionalized tetracyclic compounds l l c , l l d , and 16 were prepared from the ene-diynes 4c, 4d, and 10 by treatment with 2 equiv. of [Co,(CO),] and 4-methylmorpholine N-oxide (NMO) or Me3N0 in yields of 24, 22, and 53%, respectively (Table). In the presence of 1-3 equiv. of H,O added to the NMO used for induction of the Pauson-Khandreaction of 6d, a mixture of cyclopentanones 17/18 and cyclopentenones 12/13 was obtained (Scheme 5). The first example of a [Co,(CO),]-induced highly stereoselective ene reaction is described. To account for these results, the formation of intermediates are proposed (Schemes 6 and 7) which hitherto have not been considered in the mechanistic description of the Pauson-Khand reaction. ). Usually, this transformation is initiated by heating in solution or oxidation using 4-methylmorpholine N-oxide (NMO), trimethylamine oxide (Me,NO) or DMSO. In addition, special methods were described [5], e.g. the use of solid adsorbing materials [6] or catalysts [7]. Intramolecular cyclization-carbonylations, by which hept-1-en-6-ynes and oct-1 -en-7-ynes were transformed into bicyclo[3.3.0]oct-1-en-3-ones and bicyclo[4.3.0]non-6-en-8-ones [8], could also be achieved under these conditions. The choice of the method for activating the cyclization reaction depends on the substrate. Thus, the tetracyclic [5.5.5.5]fenestrane 2 was only formed by treatment of 1 with a trialkylamine N-oxide like NMO or Me,NO [9] (Scheme I, a).A very attractive approach to fenestranes is given by a tandem Pauson-Khandreaction of easily accessable ene-diynes. Thus, we had observed that the open-chain ene-diyne 4c reacted with 2 equiv. of [Co,(CO),] in the presence of NMO via a tandem reaction directly

Discovery of BMS-846372, a Potent and Orally Active Human CGRP Receptor Antagonist for the Treatment of Migraine

“…As such, the first successful synthetic route to racemic 5 is outlined in Scheme with the formation of a key target intermediate ketone 13 . Thus, the dienyl ketone 6 was formed by reaction of commercially available but-3-enylmagnesium bromide and pent-4-enoyl chloride . The addition of 2,3-difluorophenyl lithium generated from 1-bromo-2,3-difluorobenzene , afforded alcohol 7 in a 55% yield.…”

“…Thus, the dienyl ketone 6 was formed by reaction of commercially available but-3-enylmagnesium bromide and pent-4-enoyl chloride. 21 The addition of 2,3-difluorophenyl lithium generated from 1-bromo-2,3-difluorobenzene 22,23 afforded alcohol 7 in a 55% yield. The formation of the 7membered ring 8 was achieved by ring-closure metathesis (RCM) with benzylidene-bis(tricyclohexylphosphine)dichlororuthenium (Grubbs-I) catalyst in 89% yield under high dilution (0.012 M in CH 2 Cl 2 ).…”