RESUMO
Chiral unsaturated beta-amino alcohols possessing a dialkylamino function cyclize in the presence of Pd(II) catalysts and reoxidants to afford enantiopure bicyclic oxazolidines with total regio- and stereocontrol. The scope and limitations of this transformation have been studied.
Assuntos
Compostos Bicíclicos Heterocíclicos com Pontes/síntese química , Oxazóis/síntese química , Paládio/química , Amino Álcoois/química , Compostos Bicíclicos Heterocíclicos com Pontes/química , Catálise , Técnicas de Química Combinatória , Ciclização , Oxazóis/química , EstereoisomerismoRESUMO
Amino alcohols, having an enol ether function, cyclized in acidic medium to give quantitatively diastereosomerically pure bicyclic compounds that were transformed in five steps in enantiopure trans-5-alkylproline derivatives.
Assuntos
Amino Álcoois/química , Prolina/análogos & derivados , Prolina/síntese química , Compostos Bicíclicos com Pontes/síntese química , Compostos Bicíclicos com Pontes/química , Ciclização , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Oxirredução , Estereoisomerismo , Difração de Raios XRESUMO
New beta-amino alcohols possessing a vinylsilane moiety were reacted with glyoxal to produce lactones that were transformed in three steps in enantiopure pipecolic acid derivatives. The key step was a totally diastereoselective ene-iminium cyclization, whose mechanism can be viewed as a direct cyclization of the vinylsilane moiety onto the iminium ion. The reactivity of two beta-amino alcohols having an allylsilane terminator was also examined. Their difference of reactivity toward glyoxal can be ascribed to the intervention of a carbocation, which presents a behavior that differs according to the position of the trimethylsilyl group.
RESUMO
Diastereoselective reactions between (S)-phenylglycinol-derived oxazolidines and two unsaturated organolithium reagents afforded chiral beta-amino alcohols having vinyl and alkynylsilane moieties. When the same reactions were performed in the presence of titanium isopropoxide, a dramatic change of regioselectivity was observed, from the alpha- to the gamma-position, thus producing beta-amino alcohols with allyl or allenylsilane functions. A rationalization of the observed diastereoselectivity was suggested for each case.