Nickel-Catalyzed Highly Stereoselective Ring Opening of 7-Oxa- and Azanorbornenes with Organic Halides.
Nickel-catalyzed ring-opening reactions of 7-heteroatom norbornadienes and norbornenes with various organic halides to give products with multiple stereocenters are described. Treatment of 7-oxabenzonorbornadiene (1a) and 7-carbomethoxy-7-azabenzonorbornadiene (1b) with aryl iodides (ArI) in the presence of NiCl(2)(PPh(3))(2) and Zn powder gave the corresponding ring-opening addition products cis-1,2-dihydro-2-aryl-1-naphthol (2a-m) and methyl N-[cis-1,2-dihydro-2-aryl-1-naphthyl]carbamate (3a-e) completely stereoselectively in 40-99% yields. The nickel system also catalyzes the reaction of highly substituted oxabicyclic [2.2.1] compounds (1c-e) with organic halides (PhI, PhCH(2)Br, PhCHCHBr, and PhCBrCH(2)) to give the corresponding ring-opening products (4a-d, 5, 6a,b) that consist of four fixed stereocenters. Studies on the effect of solvent on the reaction of 1a with PhI show that CH(3)CN gives the highest yield of product 2a; no product 2a is observed when toluene, dichloromethane, methanol, DMF, or DMSO is used as solvent. Addition of extra PPh(3) to the reaction mixture reduced the yield of 2a. A mechanism is proposed to account for the formation of these nickel-catalyzed ring-opening addition products.
Feng
Chiou-Chii
CC
Department of Chemistry, National Tsing Hua University, Hsinchu 30043, Taiwan.
Nandi
Malay
M
Sambaiah
Thota
T
Cheng
Chien-Hong
CH