Triisopropylphenyl-hexahydrophosphinine oxide

The preparation of the triisopropylphenyl-hexahydrophosphinine oxide (40) required alternative synthetic methods. In the first approach, introduction of the aryl group was attempted by substitution at the phosphorus atom. The 6-ring phosphinate (37) was converted to the corresponding phosphinous chloride (38) in two steps, whose reaction with the Grignard reagent followed by oxidation led, surprisingly, to a 9 1 mixture of an O-inserted species (39) and the desired product (40) (Scheme 18) [30],... 

According to another protocol, the double-bonds of the aryl-dihydrophosphinine oxide (5t) were subjected to a stepwise saturation. In the first step, the electron-poor a,P-double-bond of the starting material (5X) was reduced via hydroboration. The remaining unsaturation and the chlorine atom in 41 were removed by catalytic hydrogenation. This method was found to be more suitable for the preparation of the triisopropylphenyl-hexahydrophosphinine oxide (40) (Scheme 19) [30],... 

Catalytic hydrogenation of 2,4,6-trialkylphenyl- and 4-alkylphenyl-l,2-dihy-drophosphinine oxides (34) afforded, in most cases, the expected hexahydrophosphinine oxides (35). However, hydrogenation of the triisopropylphenyl starting... 

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