REACTIONS OF CUMULATED AND CONJUGATED DIENES WITH SULFUR-TRIOXIDE

The reactions of a series of cumulated (la-5a) and conjugated alkadien es (8a-13a) with sulfur trioxide have been studied in the temperature range of -60 to 25-degrees-C using dichloromethane as solvent and 1.5 equiv of dioxane as reactivity moderator. Reaction of tetramethylallen e (1a) at low temperature yielded the beta-sultone lb, which at 0-degr ees-C was slowly converted into 2,4-dimethyl-1,3-pentadiene-3-sulfonic acid (1f). This conjugated dienesulfonic acid, in the presence of add itional SO3 at 0-degrees-C, was rapidly converted into the unsaturated delta-sultone 1g. Reaction of 1,2-cyclononadiene (5a) with SO3 formed an exception to the generally observed formation of the unsaturated d elta-sultones g, as at low temperatures a 1:1 mixture of 2-cyclononene -2,1-sultone (5b) and the corresponding carbyl sulfate (5d) was formed . These products at 0-degrees-C were both converted into the same alka dienesulfonic acid, viz. 6. Upon using an excess of SO3, 6 was rapidly converted into 3-cyclononene-1,2-sultone-3-sulfonic acid (7). Reactio n of the conjugated alkadienes 8a-13a with sulfur trioxide led to the formation of the similar unsaturated delta-sultones 8g-13g, as observe d upon starting with the cumulated dienes 1a-5a. The reactions of SO3 With the conjugated alkadienes 9a-12a clearly demonstrate that the for mation of the delta-sultones proceeds non-stereospecifically. The form ation of the unsaturated delta-sultones from the alkadienes la-5a and 8a-13a is, therefore, suggested to proceed via a two-step reaction, vi z. an initial [2s + 2s] cycloaddition, followed by very fast conversio n of the resulting beta-sultone into the unsaturated delta-sultone g.