New example of Ramberg-Böcklund reaction initiated by Michael addition

Abstract

Only isolated cases were reported [1–4] on the synthesis of functionalized olefins from α-haloalkyl vinyl sulfones through Ramberg–Bo..cklund reaction initiated by Michael addition. The limitations of this reaction evidently depend both on the structure of the initial substrate and on the nature of the used reagent. For instance, it was established in [5] that the treatment with potassium tert-butylate, a strong base but a weak nucleophile, of α-haloalkyl vinyl sulfones containing an allyl hydrogen atom promoted the so-called vinylogic Ramberg–Bo..cklund reaction leading to the formation of conjugated dienes. For instance, by this procedure nona-1,3diene was obtained in 72% yield proceeding from 1-(bromomethylsulfonyl)oct-1-ene. We showed in [6] that the treatment with the typical Michael reagents, enolates of CH-acids, of bromomethyl β-styryl sulfone led to the cyclization initiated by Michael addition giving tetrahydrothiophene S,S-dioxide derivative. We report here that at treating 1-(bromomethylsulfonyl)cyclohex-1-ene (I) with sodium dimethyl malonate (20°C, 17 h) from the three mentioned possible reaction routes proceeds the one consisting in the Ramberg–Bocklund reaction initiated by Michael addition: The functionalized derivative of methylenecyclohexane II is obtained. Unsaturated sulfone I was obtained in a two-stage process involving the addition of BrCH2SO2Br to cyclohexene (CH2Cl2, 10°C, 24 h, no special initiation was required) and the dehydrobromination of the adduct in a water-dioxane solution of Na2CO3 at heating (50°C, 30 h). SO2CH2Br