Radical cyclisations promoted by dimanganese decacarbonyl: A new and flexible approach to 5-membered N-heterocycles
作者:Bruce C. Gilbert、Wilhelm Kalz、Chris I. Lindsay、P.Terry McGrail、Andrew F. Parsons、David T.E. Whittaker
DOI:10.1016/s0040-4039(99)01271-x
日期:1999.8
Radical cyclisation of various unsaturated halides using dimanganesedecacarbonyl/hv has been explored. Substituted pyrrolidinones and a pyrrolidine were isolated in good to excellent yield; the radical produced on cyclisation can undergo iodine or hydrogen atom transfer, or reaction with TEMPO.
Initiation of radical cyclisation reactions using dimanganese decacarbonyl. A flexible approach to preparing 5-membered rings
作者:Bruce C. Gilbert、Wilhelm Kalz、Chris I. Lindsay、P. Terry McGrail、Andrew F. Parsons、David T. E. Whittaker
DOI:10.1039/b000835o
日期:——
Photolysis of dimanganese decacarbonyl [Mn2(CO)10] using visible light produces the manganese pentacarbonyl radical [·Mn(CO)5] which reacts with organohalides to form carbon-centred radicals. Efficient halogen-atom abstraction occurs with allylic or benzylic halides or polyhalogenated precursors bearing a weak carbon–halogen bond. Steric interactions are also important and primary halides generally react much faster with ·Mn(CO)5 than secondary or tertiary halides. The carbon-centred radicals can undergo efficient dimerisation or, in the presence of an acceptor double bond, cyclisation to form 5-membered rings. Cyclisation of terminal alkenes leads to primary radicals, which can then react by iodine- or bromine-atom transfer or, on addition of propan-2-ol, hydrogen-atom transfer. Hydroxylamines can also be formed when cyclisation reactions are carried out in the presence of TEMPO. These high-yielding cyclisation–trapping reactions are initiated under mild reaction conditions and the manganese halide by-products [of type XMn(CO)5] can be easily separated from products by a simple DBU work-up procedure.