Steric promotion of cyclization reactions: Substituent effect studies in the furan intramolecular diels-alder reaction
作者:Brian J. Mcnelis、Jeremy T. Starr、Hung Dang
DOI:10.1002/jhet.5570350649
日期:1998.11
ide compounds have been synthesized and their rates of cyclization and equilibrium product concentrations determined. Increased steric bulk on the sulfonamide substituent has been shown to increase both the rate of cyclization and yields of these reactions. A three-fold increase in rate and 15% increase in yield was observed as the substituent was varied from methyl to triisopropylbenzene.
A simple and practical protocol was developed for the synthesis of sulfonamides by reacting organometallic reagents with SO2 gas generated on demand. SO2 was generated from readily available reagents safely in a highly contained and controlled fashion. The protocol allows the synthesis of sulfonamides without using either atom-inefficient SO2 surrogates or a SO2 cylinder that requires stringent storage regulations in the laboratory. The protocol was successfully applied to the synthesis of sildenafil.
A series of palladium catalysed consecutive bis(5-exo trig)-, 5-exo trig-6-exo trig-, and 5-exo trig-7-endo trig-cyclisations via an alkene relay onto benzene or a wide range of heterocycles (pyrrole, furan, thiophen, indole, pyridine, pyridones) generates 5,5-, 5,6- and 5,7-spiroindolines in good yield.
Synthesis of <i>N</i>-Acyl-5-aminopenta-2,4-dienals via Base-Induced Ring-Opening of <i>N</i>-Acylated Furfurylamines: Scope and Limitations
N-Acylation of furfurylamines provided 1, which on double deprotonation with LDA led to the formation of N-acyl-5-aminopenta-2,4-dienals 2 via an isomerization involving opening of the furan ring. The scope and limitations of the procedure were examined by considering the influence of substituents on the carbonyl group and also on the heterocycle moiety. The efficacy of the reaction was shown to be very dependent on the nature of these groups.