Reaction of ethyl trifluoropyruvate with 2-(5-Methyl-2-phenyl-2H-1,2,3-diazaphosphol-4-yl)-4H-benzo[d]-1,3,2-dioxaphosphorin-4-one. Effect of exocyclic substituent on chemoselectivity

Abstract

Benzo[d]-1,3,2-dioxaphosphorin-4-ones (P-phosphorrylated cyclic derivatives of salicylic acid), containing a nucleophilic phosphorus atom and electrophilic endocyclic carbonyl group, exhibit a specific reactivity. They react readily to increase the ring to sevenmembered one by the action of activated systems with multiple bonds [1–6]. Introduction to the phosphorus atom of the benzo[d]-1,3,2-dioxaphosphorin-4-one an exocyclic substituent, the λσ-diazaphosphol fragment containing the P atom, could change the direction of the interaction with such activated unsaturated systems as carbonyl compounds. Indeed, it appears that the weak-acceptor and bulky diazaphosphol moiety in the compound I leads to a change of the reaction direction with ethyl trifluoropyruvate. In contrast to the ordinary derivatives of benzo[d]1,3,2-dioxaphosphorin-4-one [7], here predominates (>90%) the formation of a (Р–С → Р–ОС)-regrouping product, the 1,3,2-dioxaphosphepin derivative II involving a dioxaphosphorine fragment only. The trifluoropyruvate ester contains a prochiral carbonyl group, which is the source of the second chiral center (C), causing the formation of two diastereomers (55:45) of the reaction product II, whose structure was established by the NMR and mass spectrometry. The H, С–{H}, Р–{H} NMR spectra of the compound II purified from the volatile impurities contain a double set of signals that can not be attributed to one or other diastereomers due to their close arrangement. The minor reaction direction (<8%) is the formation of a pentacoordinated phosphorus atom derivative III, whose signals in the Р–{H} NMR spectrum are: –32.3 d, –34.1 d (5:1) (P), 254.0 br.d (P) (JРСР 87.2–87.3 Hz).