Synthesis of Organothioacrylonitriles and Organoselenoacrylonitriles by Reaction of 1-Halo-1-chalcogenoalkenes with CuCN

Functionalized alkenyl chalcogenides (S, Se and Te) have great potential in organic synthesis, since they are valuable intermediates for the selective preparation of several organic compounds.1-7 The synthesis of vinylic chalcogenides has therefore attracted the attention of several research groups, and many novel methods for their preparation have been proposed in the last years.1-7 We described practical methodologies for the preparation of vinylic chalcogenides based on Wittig and Wittig-Horner reactions.8-10 Studies on the synthesis of α-phenylseleno and α-phenyltelluro acrylonitriles and the chemical reactivity of α-phenylseleno acrylonitriles in reactions with DIBAL-H, amines and in a Diels-Alder-type reaction were also described.10 Among the functionalized vinylic chalcogenides, those containing electron withdrawing groups, like a cyano group at the sp2 carbon (α-chalcogeno-α,β-unsaturated nitriles), are of great interest since they combine the chemical reactivity of the vinyl chalcogenide and the vinyl nitrile.1 Vinylic sulfides α-substituted by strong electron withdrawing groups have been synthetically used as potent Michael acceptors,11,12 in a variety of cycloaddition reactions13-18 and in studies as precursors of extended enolates.19,20 The selenium analogs have been used as dienophiles in DielsAlder reactions,21,22 as Michael acceptors23-26 and in the synthesis of 2,3-dihydroselenophenes and butadienes.27 α-Cyano substituted vinylic sulfides have been prepared by a few different routes.28,29 Methods for the preparation of α-phenylselenoacrylonitriles are also just a few10,30 and the synthesis of the corresponding α-phenyltelluroacrylonitriles was recently described by us.10 α-Phenylselenoacrylonitriles have been prepared by the addition of benzeneselanyl chloride or bromide to cyano olefins leading to α-seleno adducts, which are subjected to in situ dehydrohalogenation.27,30,31 Recently, Chinese authors described the preparation of several α-phenylseleno-α,β-unsaturated nitriles in moderate to good yields via α-phenylselanyl cyanomethylene triphenylarsorane.32,33 However, this method is restrict to aromatic aldehydes and no mention regarding the stereochemistry of the products was made. Besides these drawbacks, this method suffers from the high toxicity of arsenium compounds. More recently, Perin et al.34 described the synthesis of α-phenylselenoacrylonitriles and α-phenylseleno-α,βunsaturated esters by Knoevenagel reaction under solventfree conditions.