Intramolecular oxyselenation of diolefins

Abstract

Reaction of cis,cis-cyclo-octa-1,5-diene, diallyl ether, or hexa-1,5-diene with copper(II) chloride and potassium selenocyanate in methanol gives smoothly 2,6-dimethoxy-9-selenabicyclo[3.3.1]nonane (1), an isomeric mixture of 3,5-bis(methoxymethyl)-1-oxa-4-selenan (2) and 3-methoxymethyl-6-methoxy-1,4-oxaselenepan (3), or an isomeric mixture of 2,5-bis(methoxymethyl)selenolan (4) and 2-methoxymethyl-5-methoxyselenan (5), respectively, in good yield. The ¹³C n.m.r. spectra of (2)–(5) revealed the presence of nearly equal amounts of two isomers in each compound, probably cis and trans with respect to the two substituents on the ring. The reaction has been revealed to proceed through methoxyselenocyanation of one double bond, followed by in situ intramolecular oxyselenation of the other in the resulting alkyl selenocyanates, lsomerizations between (2) and (3) and also between (4) and (5) were effected by hydrogen chloride in methanol through an episelenium ion intermediate, the ratios of (2) : (3) and (4) : (5) being 95 : 5 and 41 : 59 respectively at equilibrium.