Dienophiles, phosphoryl

The 4-I-2-cycloaddition of trimethylsilyl (TMS)-substituted cyclopentadiene with phosphorylated nitroso alkenes formed bicyclo 1,2-oxazines. However, as dienophiles, phosphorylated nitroso alkenes also react with cyclopentadiene and cyclohexadiene. The phosphoramidite-rhodium complex (84)-catalysed 4- -2-cycloaddition of a,fi-unsaturated imines with isocyanates produced pyrimidinones in good yields and with high enantioselectivities. ... 

Esters of a-diazoalkylphosphonic acids (95) show considerable thermal stability but react with acids, dienophiles, and triphenylphosphine to give the expected products. With olefinic compounds in the presence of copper they give cyclopropane derivatives (96), but with no such compounds present vinylphosphonic esters are formed by 1,2-hydrogen shift, or, when this route is not available, products such as (97) or (98) are formed, resulting from insertion of a carbenoid intermediate into C—C or C—H bonds. The related phosphonyl (and phosphoryl) azides (99) add to electron-rich alkynes to give 1,2,3-triazoles, from which the phosphoryl group is readily removed by hydrolysis. 

The Diels-Alder reaction of 1,2-dihydrophosphinine oxides with dienophiles, such as acetylenic derivatives and maleic acid derivatives affords 2-phosphabicyclo [2.2.2]octadiene and 2-phosphabicyclo[2.2.2]octene 2-oxides that may be regarded as the precursors of low-coordinate, methylenephosphine oxides that are useful in the phosphorylation of 0- and N-nucleophiles. It was observed that the photo-chemically induced fragmentation-related phosphorylation may follow a novel addition-elimination mechanism instead of the classical elimination-addition protocol. 

Ethyl diethoxyphosphinylpropynoate (122) can act as a good dienophile it also reacts with azides to form C-phosphorylated-l,2,4-triazoles. Amines add to l,2-bis(dialkoxyphosphinyl)acetylene to give the enamines (123) when the latter are derived from primary amines, they can be C-alkylated via their lithio derivative. ... 

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