Asymmetric synthesis of 4-formyl-1-(ω-haloalkyl)-β-lactams and their transformation to functionalized piperazines and 1,4-diazepanes
摘要:
Chiral piperazine and 1,4-diazepane annulated beta-lactams, prepared from the corresponding (3R,4S)-4-imidoyl-1-(omega-haloalkyl)azetidin-2-ones through reduction with sodium borohydride in ethanol, were transformed into novel methyl (R)-alkoxy-[(S)-piperazin-2-yl]acetates and methyl (R)-alkoxy-[(S)-1,4-diazepan-2-yl]acetates upon treatment with hydrogen chloride in methanol. On the other hand, bromination of (3R,4R)-1-allyl-4-formyl-beta-lactams and (3R,4S)-1-allyl-4-imidoyl-beta-lactams in dichloromethane, followed by sodium borohydride reduction of the resulting dibrominated azetidin-2-ones in ethanol, did not afford the envisaged bicyclic beta-lactams but unexpectedly furnished (3R,4S)-1-(2-bromo-2-propenyl)azetidin-2-ones instead. (C) 2011 Elsevier Ltd. All rights reserved.
Lewis Acid-Promoted Intermolecular Carbonyl-ene Reaction of Enantiopure 4-Oxoazetidine-2-carbaldehydes. Rapid Entry to Novel Fused Polycyclic β-Lactams
Lewisacid-promoted carbonyl-ene reaction of enantiomerically pure 4-oxoazetidine-2-carbaldehydes with various activated alkenes gives 4-[(1'-hydroxy)homoallyl]-beta-lactams with a very high level of syn diastereofacial selectivity. The above homoallylic alcohols are used for the diastereoselective preparation of fused bicyclic, tricyclic, and tetracyclic beta-lactams of nonconventional structure using
Concise, Divergent β-Lactam-based Route to Indolizidine and Quinolizidine Derivatives via Sequential Regio- and Stereocontrolled Intramolecular Nitrone-alkene Cycloadditions
作者:Benito Alcaide、Carmen Pardo、Elena Sáez
DOI:10.1055/s-2002-19333
日期:——
A novel, concise, divergent methodology to both indolizidine and quinolizidine systems based on the sequential regio- and stereocontrolled intramolecular nitrone-alkene cycloaddition (INAC) reactions of 2-azetidinone-tethered alkenylaldehydes is reported.
The synthesis of novel 4-(5'-pynolidinyl)-beta-lactams from imines derived from 4-formyl-beta-lactams and alpha-amino esters via cascade imine-->azomethine ylide-->1,3-dipolar cycloaddition reactions is described. These cascades are endo-specific, exhibit facial stereoselectivity and occur in good to excellent yields. (C) 1999 Elsevier Science Ltd. Ail rights reserved.