Preparative and theoretical study on chain length-dependence and substrate selectivity in the cycloalkylation of condensed [1,2,4]triazolo[4,3-b]pyridazine-6(5H)-one-3(2H)-thiones
                                
                                    
                                        作者:Antal Csámpai、Mónika Simó、Zoltán Szlávik、András Kotschy、Gábor Magyarfalvi、György Túrós                                    
                                    
                                        DOI:10.1016/s0040-4020(02)01156-0
                                    
                                    
                                        日期:2002.10
                                    
                                    Cyclization of condensed [1,2,4]triazolo[4,3-b]pyridazine-3(2H)-6(5H)-ones with alpha,omega-dibromoalkanes afforded a series of novel ring systems including zwitterions and isomeric tetracyclic lactams. The product distribution is controlled by the chain-length of the reagent, the polarity of the solvent and the structure of ring A in the substrate. The observed substrate selectivity was interpreted on the basis of amide-I IR frequencies and by the results of ab initio B3LYP DFr calculations carried out at 6-31 G and 6-31 G(d) basis sets using IPCM solvation model. The cycloalkylation with 1,4-dibromobutane gave also macrocyles as detectable by-products which underwent ring contraction yielding lactams on attempted chromatographic separation. (C) 2002 Elsevier Science Ltd. All rights reserved.