Reaction of 4-aryl-2,6-dichlorobenzo[e[1,2]oxaphosphinine 2-oxides with organomagnesium compounds as a convenient synthetic approach to (Z)-dialkyl(aryl)[2-(2-hydroxyaryl)-2-arylethenyl]phosphine oxides

We recently prepared benzo[e][1,2]oxaphosphinine 2-oxides [1, 2], phosphorus analogs of coumarins which are widespread in nature and possess diverse biological activity [3]. The chemical behavior of this class of compounds is comparatively poorly studied. Thus it was shown that they fairly readily chlorinated [4] and brominated [5] into the heterocyclic fragment to form finally 3-halo derivatives. In the present work we investigated for the first time reactions of 4-aryl2,6-dichlorobenzo[e][1,2]oxaphosphinine 2-oxides I with organomagnesium reagents (Grignard reagents). Taking into account the data summarized in the monograph [6], we expected that the reactions would lead to 2-alkyl(aryl)-4-aryl-6-chlorobenzo[e][1,2]oxaphosphinine 2-oxides II which attract some interest as complexing agents for rare metals. However, phosphinines I were found to react unambiguously with a double excess of Grignard reagents to give functionally substituted phosphine oxides III in quantitative yields. At an equimolar ratio of the starting reagents, mixtures of phosphinines II, phosphine oxides III, and 2-hydroxy-4-aryl-6-chlorobenzo[e][1,2]oxaphosphinine 2-oxides IV formed. It is obvious that Grignard reagents almost equally reactive toward DOI: 10.1134/S1070363208060340