Stereoselective sequential photochemical cycloaddition - iminium ion - propargylsilane cyclization. Synthesis of quinolizidines and pyrido [1,2-a]azepines
摘要:
Photochemical cycloaddition of the enaminecarbaldehydes 15 and 16 with the acrylic acid derivatives 20a-c gave the 2-hydroxytetrahydropyridines 21a-c and 24a-c, respectively which cyclize on treatment with trifluoroacetic acid or Lewis acids to furnish the quinolizidines 22a-c and pyrido[1,2-a]azepines 25a-c, respectively in good yields and with high 1,3-induced diastereoselectivity. Indolizidines 27 cannot be prepared by this method.
Completely regioselective α-acyliminium ion cyclizations with allyl and propargyl silanes
作者:Henk Hiemstra、W.Nico Speckamp
DOI:10.1016/s0040-4039(00)81668-8
日期:1983.1
Intramolecular reactions of α-acyliminium ions with allyl and propargyl silanes occur under the influence of trifluoroacetic acid, to afford in high yield and with complete regioselectivitybridgehead nitrogen bicyclic compounds – .
The domino-Heck double cyclisation of the arylbromides 1, which contain an allylsilane and an alkyne moiety and are easily accessible by an addition of the corresponding lithiated alkynes 5 to the aldehydes 4, leads to the tetrasubstituted alkenes 2 and 3 in good yield. The reaction produces exclusively compounds with an E double bond and additionally proceeds with good to excellent induced diastereoselectivity