Phosphate monoesters reduction

The [l,4,2]-oxazaphosphinane naphthoquinones 51 were obtained from a short synthesis based on transformation of 2,3-dichloro-l,4-naphthoqui-none into 2-amino-3-hydroxy-1,4-naphthoquinone 50 by a double Michael addition of water and of nitrite, followed by the reduction of the nitro group into an amino group using sodium dithionite (Scheme 11). Then, a three component reaction, mixing various ketones, alkyl dichloro-phosphate, and quinone 50 furnished fused the quinonic systems 51 in yields ranging from 60% to 95%. The monoester derivative 52 is readily obtained by treatment of the ester 51 ((R = Et, = R = Me) with TMSBr in chloroform, followed by methanolysis of the sdyl ester intermediate. 

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