HOMOCOUPLING OF ALKYL-HALIDES AND CYCLIZATION OF ALPHA,OMEGA-DIHALOALKANES VIA ACTIVATED COPPER

The homocoupling of alkyl halides utilizing a highly activated form of zerovalent copper has been studied. Allyl and benzyl halides produce high yields of their respective homocoupled dimers 1,5-hexadiene and 1,2-diphenylethane. An 83% yield of tetradecane was produced from n-heptyl iodide. The yield drops substantially for the corresponding bromo and chloro compounds. The yield is also strongly solvent and temperature dependent. Secondary and tertiary alkyl iodides and bromides produce moderate to low yields of homocoupling accompanied by substantial amounts of the corresponding alkane and alkenes. The copper-mediated cyclization of α,ω-di-haloalkanes has also been examined. The yield of cycloalkanes is moderate to high for the smaller rings with the yield decreasing substantially as the ring size increases. The compound meso-l,2-dibromo-l,2-diphenylethane was found to produce exclusively trans-stilbene in high yield. The activated copper was produced by reducing cui-pr3with a preformed solution of lithium naphthalenide. Complexes using triethylphosphine and tri-n-butylphosphine were both studied. The product yields were found to be similar in both cases. © 1990, American Chemical Society. All rights reserved.