Abstract

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Reaction of cymantrene (6) with n-butyllithium followed by benzophenone and subsequent hydrolysis yielded 1-(diphenylhydroxymethyl)(η5-cyclopentadienyl)(tricarbonyl)manganese (7). Treatment of 7 with HBArF·2Et2O in methylene chloride affords the blue cation 2b. Investigations of single crystals of 2b by means of the X-ray technique showed a displacement of the exo carbon by 6.6° toward the metal and a pronounced bond alternation of the C−C bonds of the fulvene moiety. DFT calculations on the parent system 2a and on a system with a planar fulvene moiety (2a‘) yielded an energy difference of 23 kJ/mol in favor of 2a. As a result of the bending of the exo methylene group the positive charge at the metal is increased and at C9 decreased.

Asymmetric Pd-catalyzed allylic alkylations of dimethyl malonate and diethyl 2-acetoxymalonate with 3-chlorocyclopentene, using phosphanyloxazolines 1 and ent-1 as chiral ligands, gave products (−)-2 and (+)-3b with 95 and 99.5% ee, respectively. Oxidative degradation of (+)-3b furnished (+)-(R)-cyclopent-2-ene-1-carboxylic acid [(+)-4] with Ͼ 99% ee. Alkylation product (−)-2 was transformed into enantio-

Mechanistic considerations made a decisive contribution to the development of new chiral P,N ligands L* containing tricarbonylcyclopentadienylmanganese (cymantrene). These ligands induce very high enantioselectivities (>99:1) in allylic substitutions of cyclic substrates 1 with formation of 2 (2-Bp=2-biphenylyl).