Reactions of Diazomethane with Sulfonyl-activated Double Bonds

The cyclo-addition reaction of diazomethane with a,/3-unsaturated sulfones is described. Divinyl sulfone and phenyl vinyl sulfone give 1or 2-pyrazolines depending on the reaction conditions. cisand /rans-l,2-Bis(methylsulfonyl)ethene form pyrazolines, which on reaction with either triethylamine or excess of diazomethane lead to substituted pyrazoles. The addition of diazomethane to doüble bonds activated by electron-withdrawing substituents such as carbonyl, nitro and nitrile is a well-documented route to substituted pyrazolines.1 However, the addition of diazomethane to a,/3-unsaturated sulfones is scarcely mentioned. Parham et al.2 reported the formation of two types of pyra­ zolines from a,/3-unsaturated sulfones and diazo­ methane viz a normal addition product in which the C atom of the diazomethane is attached to the /3-C of the vinyl sulfone and an abnormal product with the diazocarbon attached to the a-C of the unsaturated system. It is generally accepted1 that the initial reaction products of diazomethane with activated double bonds are 1-pyrazolines, which however, may undergo a facile prototropic rearrangement to the corresponding 2-pyrazolines during crystallization, by gently warming or by a trace of acid or base.1® Backer et al.3 reported thattreatment of thiophene1,1-dioxides with excess of diazomethane gave rise to addition of diazomethane to only one double bond of the thiophene-1,1-dioxides. We investigated the reaction of divinyl sulfone (1) —an open chain analogue of the thiophene-1,1dioxides—with diazomethane under similar con­ ditions and we found that instead of one, both double bonds of 1 reacted smoothly. Treatment of divinyl sulfone (1) with a basefree ethereal solution of diazomethane gave the 1-pyrazoline 2 as a mixture of the meso and dl form in yields up to 90%. In the presence of a trace of triethylamine the 2-pyrazoline 3 was obtained in 76% yield. Heating of 2 in acetonitrile in the presence of a little of triethylamine gave a quanti­ tative rearrangement to 3 (Scheme 1). “Present address: Unilever Research Laboratory, Duiven, The Netherlands. 6Present address: Department of Organic Chemistry, University at Nijmegen, Toemooiveld, Nijmegen, The The Netherlands. To whom correspondence should be addressed. *^S0 2>j*