Structure and reactivity of .alpha.,.beta.-unsaturated ethers. 16. Electrophilic addition of benzenesulfenyl chloride to .alpha.,.beta.-unsaturated ethers and sulfides

Abstract

The rates of addition of benzenesulfenyl chloride to ,/3-unsaturated ethers and sulfides have been measured in CCU at 30 °C. Reactivities of alkyl vinyl ethers and sulfides increase with the electron donating ability of alkyl group, p* being -5.4 and -1.7, respectively. /3-Alkyl and /3-methoxy substitutions enhance the reactivity of vinyl ether while -methyl substitution influences it little. Adducts are exclusively the Markownikoff type. With ethyl propenyl ethers, anti addition is slightly dominant over syn addition. It was concluded from these results that the rate-determining transition state resembles a symmetrically bridged sulfonium ion intermediate 23 and that an open carbonium ion mediates between the rate-and product-determining steps.

Total Syntheses of Pumiliotoxin A and Allopumiliotoxin Alkaloids. Interplay of Pharmacologically Active Natural Products and New Synthetic Methods and Strategies

“…Indolizidine vinyl epoxide 110 was then generated by hydroxyl-directed epoxidation of the trifluoroacetate salt of 111 , while its alkylation partner 117 was derived from the known ylide 35 21 and phenylthioethanal ( 116 ) . The Pd(0)-mediated alkylation again benefited from the addition of water and gave a single alkylideneindolizidine 118 in 24% yield after reductive desulfonylation (Scheme ).…”

“…Indolizidine vinyl epoxide 110 was then generated by hydroxyl-directed epoxidation of the trifluoroacetate salt of 111, while its alkylation partner 117 was derived from the known ylide 35 21 and phenylthioethanal (116). 76 The Pd(0)-mediated alkylation again benefited from the addition of water and gave a single alkylideneindolizidine 118 in 24% yield after reductive desulfonylation (Scheme 24). The perfect chirality transfer from C(6) to C (11) The Trost-Scanlan synthesis of allopumiliotoxin 339B (103) was accomplished in only 11 steps from N-(tert-butoxycarbonyl)-L-proline.…”

Substituent dependence of the selectivity in alkene bromination through bromocarbenium ions

“…The strong electrondelocalizing ability of the ethoxy and phenyl groups does not lead necessarily to an open transition state, since a bridged sulfonium transition state is observed for these two groups in ArSCl addition 21. However, the values of the + constants of the acetoxy, ethoxy, and phenyl groups (-0.48, -1.10, and -0.29) indicate that the first two groups are best able to stabilize positive charge.…”