Efficient Preparation of TMSCCl2 Br and Its Use in Dichlorocyclopropanation of Electron-Deficient Alkenes.
The reaction of excess TMSCl and LiCCl2 Br at low temperature is a technically simple high yield route to TMSCCl2 Br. 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 expulsion. For nitrostyrenes the reaction arrests at the 1,4-addition product. Low temperature NMR spectroscopy 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.
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. darren.lee@nottingham.ac.uk.
Darren S
DS
Lee
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
María Jesús
MJ
Durán-Peña
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
Laurence
L
Burroughs
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. simon.woodward@nottingham.ac.uk.
Simon
http://orcid.org/0000-0001-8539-6232
S
Woodward
Michael addition; cyclopropanation; cyclopropane; dichlorocyclopropane; synthetic methods