Nonalkenic

Perhaps one of the most intriguing examples of oxirane formation with the sodium dichromate reagent is the conversion of (163) to the bisoxirane (164) (Equation (12)). The high degree of strain in this system seems to be at least partially responsible for the formation of (164) from its nonalkenic precursor <87TL353l>. 

Anhydro-compounds - Methyl 2,6-anhydro-a-D-mannofuranosldeand the nonalkenic cyclic trlmer (13) of levoglucosenone. 

With the aim of determining if similar reactivity could be displayed with maleimides using nonalkene substrates, the same authors have discovered a new photochemically mediated intramolecular [5+2] photocycloaddition of maleimides to C=N bonds [94]. Indeed, introducing a C=N based functionality to the maleimide photosubstrates 88 had the potential to extend the scope of the [5+2] cycloaddition by enabling the formation of 1,3-diazepines 89, constituting a class of diazepines that has rarely been reported. As shown in Scheme 20.38, the reaction performed in acetonitrile was tolerant to a wide range of C=N systems, and proceeded efficiently even with bulky substituted hydrazones and oximes. This process constituted a new method for the synthesis of fused polycyclic 1,3-diazepines. 

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