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A combined theoretical and experimental study of a Povarov‐type cycloaddition reaction suggests an asynchronous concerted process that is favored by double Lewis acid activation with BF3·Et2O; endo selectivity was observed in the reactions between N‐(3‐pyridyl)aldimines and styrene, cyclopentadiene, or indene, and substituted tetrahydro‐1,5‐naphthyridine derivatives were obtained in a regio‐ and stereoselective fashion.

The mechanism of the aza-Wittig reaction between phosphazenes and aldehydes has been studied computationally, using DFT methods (B3LYP/6-31G level), and experimentally. It has been found that the reaction consists of a tandem [2+2] cycloaddition-cycloreversion sequence in which pi and sigma orbitals as well as lone pairs are involved. Both [2+2] processes take place via thermally allowed supra-supra mechanisms. P-trimethyl-lambda(5)-phosphazenes are predicted to be more reactive than their P-triphenyl analogues. The stereochemical outcome of the whole reaction depends only on the second step, because conformational changes in the intermediate 1,3,2-lambda(5)-oxazaphosphazetidines have a much lower activation energy than the second [2+2] cycloreversion reaction. Preferential or exclusive formation of the corresponding (E)-imines is predicted.

N-Vinylic phosphazenes 4 are obtained by reaction of phosphorus ylide 5 and nitriles 6. Aza-Wittig reaction of phosphazenes 4 with aldehydes leads to the formation of 2-azadienes 1, which are easily converted into isoquinolines 2. Reaction of conjugated phosphazenes 4 with ethyl glyoxalate affords 5,6-dihydro-2H-1,3-oxazines 9 in a regio-and stereoselective fashion, while heterodienes 1 react with ethyl glyoxalate and diethyl ketomalonate giving 1,3-oxazines 11 and 12.