Efficient preparation of TMSCCl2Br and its use in dichlorocyclopropanation of electron deficient alkenes
Lee, Darren S. and Durán-Peña, Maria Jesus and Burroughs, Laurence and Woodward, Simon (2016) Efficient preparation of TMSCCl2Br and its use in dichlorocyclopropanation of electron deficient alkenes. Chemistry - a European Journal, 2016 (22). ISSN 1521-3765
The reaction of excess TMSCl and LiCCl2Br at low temperature is a technically simple high yield route to TMSCCl2Br. The latter is a stable source of the dichlorobromomethide carbanion, which undergoes 1,4-addition with cyclic nitroalkenes and (E)-fumarates leading to dichlorocyclopropanes after bromide explusion. For nitrostyrenes the reaction arrests at the 1,4-addition product. Low temperature NMR studies and DFT calculations suggest the formation of an ‘ate’ species [(nitronate)SiFMe3]- which, upon boil off of TMSF at 10 - 20 °C, yields the cyclopropane. DFT calculations also support the experimental differences between fluoride and acetate as promotors.
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