New chiral dipyridine N-monoxides and N,N′-dioxides, which possess an isopropylidene backbone between two pyridine rings, have been prepared from naturally occurring monoterpenes. Their utility as organocatalysts has been demonstrated in the enantioselective addition of allyltrichlorosilane to aldehydes. Enantioselectivities up to 85% ee have been obtained.
Chiral pyridine N-oxides derived from monoterpenes as organocatalysts for stereoselective reactions with allyltrichlorosilane and tetrachlorosilane
作者:Giorgio Chelucci、Salvatore Baldino、Gerard A. Pinna、Maurizio Benaglia、Laura Buffa、Stefania Guizzetti
DOI:10.1016/j.tet.2008.05.105
日期:2008.8
The synthesis of enantiomerically pure C-2-symmetric dipyridylmethane ligands and related N,N'-dioxides is reported. A procedure for the synthesis of a few new enantiomerically pure C-2-symmetric pyridine N-oxides and the preparation of four pyridine N-oxides with oxygen and nitrogen atoms as further coordinating elements in the heterocycle framework is described. All compounds were prepared from naturally occurring monoterpenes. These new compounds were assessed as organocatalysts in two different reactions, namely the allylation of aldehydes with allyltrichlorosilane that afforded homoallylic alcohols in good yields and up to 85% ee and the stilbene oxide opening by the addition of tetrachlorosilane that gave chlorohydrin in quantitative yield and up to 70% ee. (C) 2008 Elsevier Ltd. All rights reserved.
Modular pyridine-type P , N -ligands derived from monoterpenes: application in asymmetric Heck addition
作者:Andrei V Malkov、Marco Bella、Irena G Stará、Pavel Kočovský
DOI:10.1016/s0040-4039(01)00369-0
日期:2001.4
Novel (diphenylphosphinophenyl)pyridine ligands (+)-8, (+)-15, (-)-21, and (-)-26 were synthesized from (-)-beta -pinene, (+)-3-carene, (+)-2-carene, and (-)-alpha -pinene, respectively, via Krohnke annulation as the key step, and shown to effect less than or equal to 88% ee in Heck addition (27 --> 28). Ligands (+)-15 and (-)-21 are quasi-enantiomeric; ligands 8 and 26 can be prepared in both enantiomeric forms from (+)- and (-)-enantiomers of alpha- and beta -pinene, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.