Synthesis of Pyrrole Derivatives from 5,6-Dihydro-4H-1,2-oxazines via Reductive Deoxygenation by Use of Fe3(CO)12

Article abstract of DOI:10.1246/bcsj.63.3595

α-Bromooximes such as α-bromoacetophenone oxime and ethyl 3-bromo-2-(hydroxyimino)propanoate react with enamines to give 5,6-dihydro-4H-1,2-oxazines in good yields.Dihydro-1,2-oxazine derivatives are also obtained by the reaction of α-bromooximes with vinyl ethers and silyl enol ethers in the presence of Na2CO3.Dihydro-1,2-oxazines can be converted into pyrrole derivatives via reductive deoxygenation by treating with Fe3(CO)12 in moderate to excellent yields.Iron carbonyl complexes other than Fe3(CO)12 are also effective for the pyrrole-forming reaction.The efficiency of the complexes for this reaction decreases in the or der: Fe3(CO)12 >> Et3NH > Fe2(CO)9 >> Fe(CO)5.Both of the dihydro-1,2-oxazine- and pyrrole-forming reactions can be carried out in a single flask, giving pyrrole derivatives in good yields.