Aza-Wittig reaction of N-vinylic phosphazenes with carbonyl compounds. Azadiene-mediated synthesis of isoquinolines and 5,6-dihydro-2H-1,3-oxazines

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.