Diastereoselective Lewis acid-catalysed 4+2 cycloadditions of 3-alkyl-, 3-aryl- and 3-carboxyl-2H-azirines: a route to aziridine containing azabicyclo 4.1.0 heptanes and azatricyclo 2.2.1.0 nonanes

Diastereoselective Lewis acid-catalysed 4+2 cycloadditions of 3-alkyl-, 3-aryl- and 3-carboxyl-2H-azirines : a route to aziridine containing azabicyclo 4.1.0 heptanes and azatricyclo 2.2.1.0 nonanes

QC 20100525
3-Substituted-2H-azirines have been employed as 2pi components in Lewis acid-catalysed hetero Diels-Alder reactions with a variety of diene systems. A series of Lewis acids were screened for catalytic behaviour in the reaction between Danishefsky's diene and 3-phenyl-2H-azirine to give the cycloaddition adduct, and in most cases elevated temperature were required to effect cycloaddition. A noteworthy exception was a BF3.Et2O-catalysed cycloaddition which proceeded in less than I h between -70degreesC and -60degreesC. The cycloadditions were found to proceed with endo selectivity providing a single diastereoisomeric product. Benzyl 2H-azirine-3-carboxylates were found to be activated by Lewis acids and participate in endo selective cycloadditions at -20degreesC.

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