Síntese de adutos de Michael contendo um grupo organocalcogênio, sulfetos vinílicos e telurocarboidratos utilizando PEG-400

Abstract

In this present work, PEG-400 was used as green solvent to synthetized several Michael adducts containing an organochalcogen group in β-position, furnishing the corresponding products in moderate to good yields. This simple and general methology involves the addition of diorganyl dichalcogenides by reductive cleavage with NaBH4 to α,β-unsatured compounds (Scheme 1). Additionally, was performed the synthesis of the α,β-unsatured carbonyl compounds containing the thiolorganyl group at β position using PEG-400 as recyclable solvent in catalyst-free conditions (Scheme 2). This simple protocol afforded the respectives alkenyl esters and ketone in good yields and gave predominantly the Z configuration in a ratio Z:E between 69:31 to 93:17. However, only the alkenyl aldehyde derivative provided the E stereoisomer most in a Z:E ratio of 14:86. PEG-400 was reused in up 5 successive reactions without previous treatment and the adduct 6a was obtained in 87, 85, 80, 73 and 68% yields respectively, affording predominantly the (Z)-stereoisomer 6a in a Z:E ratio = 86:14 to 80:20. Finally, was performed the syhthesis of Te-carbohydrates in two steps. The cyclization was the first step and was used PEG-400 as solvent. The deprotection was the second step and was performed using water and dichloromethane (DCM) in acid media (Scheme 3). This methodology afforded Te-carbohydrates in moderate to good yields (52-76 %). Additionally, trans-dihydroxytellurolane 14 was synthesized by addition of an aqueous solution of NaHTe, generated in situ from NaBH4, to 1,3-butadiene bisepoxide 10 to give trans-3,4-dihydroxytetrahydro tellurophene 11 in excellent yield of 98% in a reaction time of 1 h.