[60164-96-7] · C8H13Cu · (R)-4-Methylcyclohexylidenemethylcopper · (MW 172.76)
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.
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.
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.
R. Bruce Banks
University of North Carolina at Greensboro, NC, USA