The 1, n-Rearrangement of a Sulfonyl group and its Utilization for Synthesis of Conjugated

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This project is to extend the 1, 3-rearrangement of a sulfonyl group in a sulfenylated allylic system to l, n-rearrangement which is applied to a new and convenient synthesis of conjugated polyenyni carbonyl compounds. At first, polyenes having methylthio and p-tolylsulfonyl groups at alpha position[2 ; R^2(MeS)(PToISO_2)C(CH=CH)mR^1 are derived from easily available methylthiomethyl P-tolyl sulfone(1). Treatment of these polyenes(2)with weak acids such as silica gel is expected to induce I. n-rearrangement of the sulfonyl group leading to 1-methylthio-n-(p-tolylsulfonyl)alkapolyenes[3 ; R^2(MeS)CH=CH(CH=CH)_<m-1>CH(PTolSO_2)R^1 which are synthetic precursors. of polyenyl carbonyl compounds. During the present project, the cases of n = 5, 7, and 9(m = 2, 3. and 4, respectively)were investigated.1. Preparation of the precursor(2)for I. n-rearrangement of a sulfonyl group : The anion of a trimethylsilylated I reacted with unsaturated aldehydes to afford 1-methylthio-l-(p-tolylsulfonyl)al … More kapolyenes[4 ; (MeS)(P-TolSO_2)C=CH(CH=CH)_<m-1>CH_2R^l. When 4 was treated with potassium t-butoxide in THF, an anion was generated. Protonation or alkylation(treatment with an alkyl halide)of the anion gave 2(R^2 =H and alkyl, respectively). As unsaturated aldehydes, 2-enal, 2.4-dienal. and 2, 4, 6-trienal could be utilized.2.1, n-Rearrangement of a sulfonyl group in 2 and synthesis of conjugated polyenones and polyenals : Elution of 2(m = 2 and 3)through column packed with silica gel gave the rearrangement product(3 ; m = 2 and 3, respectively). On similar treatment of 2(m = 4), the 1, 9-rearrangement of a sulfonyl group took place, but the yield was relatively low. Good yield of 3(m = 4)was attained by stirring of 2(m = 4)along with a small amount of silica gel in chloroform. The mechanism of the l. n-rearrangements was also investigated in a detail to reveal that the sulfonyl group dissociates as a sulfinate ion and recombine again with the resulting polyenyl cation.The expected polyenyl carbonyl compounds were obtained by alkylation of 3 with NaH and an alkyl halide followed by hydrolysis with hydrochloric acid. Less