Sodium borohydride, reaction with ozonides

A novel fragmentation of iV-arylidene- or Al-(aLkylideneamino)- 8-lactams can be induced by ozone to lead to various enol ethers after a reductive workup with sodium borohydride. The starting 8-lactams can be prepared via [2 + 2] cycloaddition of alkoxy ketenes and an azine and upon treatment with ozone at low temperature, yield the expected secondary ozonides (eq 59). Reduction of the ozonide leads to the corresponding N-nitroso intermediate, which is susceptible to fragmentation of the C4—N1 bond to give a zwitterion intermediate that rearranges to yield the product enol ethers. In the reaction sequence, fra 5- 8-lactams yield predominantly the E-enol ether while the d5- 8-lactams preferentially form the Z-configured enol ethers. 

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