[60164-96-7]  · C8H13Cu  · (R)-4-Methylcyclohexylidenemethylcopper  · (MW 172.76)

(optically active vinylcopper reagent;1 useful in stereospecific synthesis of axially dissymmetric dienes and alkenes1,2)

Solubility: dark black suspensions of the reagent (0.26 M) have been prepared in THF-pentane.1,2

Preparative Methods: (-)-(R)-(4-methylcyclohexylidene)methyl bromide3,4 in THF is treated with s-Butyllithium in pentane at -75 °C to give a solution of (R)-4-methylcyclohexylidenemethyllithium. Addition of 1 equiv of Copper(I) Iodide to this mixture, followed by stirring at -35 °C for 30 min, gives a dark black suspension of (R)-4-methylcyclohexylidenemethylcopper (eq 1).2 (S)-4-Methylcyclohexylidenemethylcopper may be prepared from (+)-(S)-(4-methylcyclohexylidene)methyl bromide3,4 using a similar procedure.1,2

Handling, Storage, and Precautions: the reagent is prepared under inert gas atmosphere at temperatures of -35 °C or below. Upon heating to rt, or exposure to oxygen, the reagent decomposes with formation of bis(4-methylcyclohexylidene)ethane. Use in a fume hood.

Oxidative Coupling: Synthesis of Optically Active Dienes of Biaxial Dissymmetry.

Alkenylcopper reagents undergo thermal or oxidative coupling to give 1,3-dienes with retention of configuration at the alkenic bond.5 Passage of a stream of oxygen through a solution of (R)-4-methylcyclohexylidenemethyl-copper affords (aR,aR)-bis(4-methylcyclohexylidene)ethane in 30% yield (eq 2).1,2 The dissymmetry of the latter compound results from the combination of two chiral alkenic axes which are oriented in a planar transoid conformation. The chiroptical properties of this and closely related planar acyclic 1,3-dienes have been reported.2,6 Additional members of this novel class of optically active dienes could be synthesized by oxidative coupling of analogous chiral vinylcopper reagents.

Alkylation: Formation of Optically Active 4-Methylcyclohexylidenealkanes.

Alkenylcopper reagents can be alkylated by treatment with alkyl halides and other electrophiles.7 Reaction of (S)-4-methylcyclohexylidenemethylcopper (enantiomer of the title reagent) with Iodomethane gives (+)-(S)-4-(methylcyclohexylidene)ethane with 98% retention of configuration (eq 3).1,2 Alkylation of (R)-4-methylcyclohexylidenemethylcopper with methyl iodide and other alkyl halides is expected to show similar stereospecificity.

1. Banks, R. B.; Walborsky, H. M. JACS 1976, 98, 3732.
2. Walborsky, H. M.; Banks, R. B.; Banks, M. L. A.; Duraisamy, M. OM 1982, 1, 667.
3. Perkin, W. H.; Pope, W. J. JCS 1911, 99, 1510.
4. Solladie, G.; Zimmermann, R. G. TL 1984, 25, 5769.
5. (a) Normant, J. F. S 1972, 63. (b) Kaufmann, T. AG(E) 1974, 13, 291.
6. (a) Duraisamy, M.; Walborsky, H. M. JACS 1983, 105, 3252. (b) Duraisamy, M.; Walborsky, H. M. JACS 1983, 105, 3264. (c) Duraisamy, M.; Walborsky, H. M. JACS 1983, 105, 3270. (d) Reddy, S. M.; Goedken, V. L.; Walborsky, H. M. JACS 1986, 108, 2691. (e) Gawronski, J. K.; Walborsky, H. M. JOC 1986, 51, 2863.
7. (a) Posner, G. H. OR 1974, 22, 253. (b) Lipshutz, B. H.; Sengupta, S. OR 1992, 41, 135.

R. Bruce Banks

University of North Carolina at Greensboro, NC, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.