Synthesis of seven-membered lactones via nickel- and zinc-catalyzed highly regio- and stereoselective cyclization of 2-iodobenzyl alcohols with propiolates.
A new class of substituted seven-membered lactones 3 were conveniently synthesized via cyclization of o-iodobenzyl alcohol 1 (o-IC(6)H(4)CH(2)OH) with various propiolates 2 (RC triple bond CCOOMe) in the presence of Ni(dppe)Br(2) and Zn powder in acetonitrile at 80 degrees C. The catalytic reaction is highly regio- and stereoselective affording seven-membered lactones in moderate to good yields. This methodology can be successfully extended to various substituted o-iodobenzyl alcohols. An intermediate 7 was obtained from the reaction of 1a with methyl 2-octynoate (2a) in the presence of Ni(dppe)Br(2) and Zn at room temperature. A mechanism involving an unusual E/Z isomerization of the carbon-carbon double bond of 7 prior to lactone formation is proposed to account for the catalytic reaction.
Rayabarapu
Dinesh Kumar
DK
Department of Chemistry, Tsing Hua University, Hsinchu, Taiwan 300.
Cheng
Chien-Hong
CH
D000480:Alkynes / Q000737:chemistry*; D001592:Benzyl Alcohols / Q000737:chemistry*; D002384:Catalysis; D007783:Lactones / Q000138:chemical synthesis*; D009532:Nickel / Q000737:chemistry*; D011422:Propionates / Q000737:chemistry*; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry*
D000480:Alkynes; D001592:Benzyl Alcohols; D007783:Lactones; D011422:Propionates; D009532:Nickel; D015032:Zinc; C011537:propiolic acid