Solvomercuration-Demercuration. 9. Oxymercuration-Demercuration of Chloro-, Epoxy-, and Thiomethyl-Substituted Alkenes

Article abstract of DOI:10.1021/jo00318a019

The oxymercuration-demercuration (OM-DM) of allyl, crotyl, 3-buten-1-yl, 4-penten-1-yl, and 5-hexen-1-yl chlorides and methyl sulfides as well as 3,4-epoxy-1-butene, 4,5-epoxy-1-pentene, and 5,6-epoxy-1-hexene has been studied.Allyl chloride undergoes a slow but normal OM to give the Markovnikov oxymarcurial.However, in situ demercuration under the standard conditions (NaOH, NaBH4) gives only allyl alcohol.Fortunately, demercuration with an ethanolic solution of sodium borohydride results in high yields of the chlorohydrin accompanied by small amounts of propylene oxide.In contrast, crotyl chloride fails to give any products resulting from the OM-DM sequence.Thus, 3-buten-2-yl chloride underwent only solvolytic reaction while 2-methylallyl chloride underwent exclusive OM to give, upon DM, the expected Markovnikov chlorohydrin.Similarly, 3-buten-1-yl chloride underwent exclusive hydration under the standard OM-DM conditions.In the case of 4-penten-1-yl chloride, the C1-C5 neighboring-group participation was seen during OM.However, 5-hexen-1-yl chloride showed exclusive hydration to give a 94percent yield of the Markovnikov chlorohydrin.The approximate rates of solvolysis of a series of representative alkyl halides have been determined under the OM conditions.The OM-DM of 3,4-epoxy-1-butene proceeded to give hydrated products although the yield was low, ca. 60percent.On the other hand, 4,5-epoxy-2-pentene gave products arising only from participation of the epoxide ring in the OM stage.Moreover, the yields of these products are very low, only ca. 15percent.By contrast, the OM-DM of 4,5-epoxy-1-pentene proceeds cleanly, giving a 96percent yield of the Markovnikov epoxy alcohol.In the case of 5,6-epoxy-1-hexene, ca. 80percent of the products arise from epoxide participation in the OM stage.With the exception of the crotyl derivative, the (methylthio)alkenes undergo hydration cleanly, although slowly, to give approximately 70-80percent yields of the thio alcohols.The crotyl alkene gave 3-butene-2-ol in only ca. 20percent yield.