Cycloaddition of PTAD to 7-methylenenorbornene (1 a) afforded the rearrangement urazole 2a, but not with 7-(pheny1methylene)norbornene (1 b) and 7-(chloromethylene)norbornene (lc). Instead, besides the [2 + 23 cycloadducts 3b and 3c, respectively, l b gave the double [4 + 23 adduct 4b and l c the novel urazole 5c (major product). 'H NMR spectroscopy (NOE) was helpful in defining the stereochemistry of the cycloadducts 3b,c and 4b, while X-ray analysis was essential in determining the structure of the unusual rearrangement product 5c. Ungewohnliche Umlagerungsprodukte bei der Cycloaddition von 4-Phenyl-4H-1,2,4-triazol-3,5dion (PTAD) an substituierte 7-Methylennorbornene Cycloaddition von PTAD an 7-Methylennorbornen (la) fiihrt zum Urazol 2a. Dagegen wird mit 7-(Phenylmethy1en)norbornen (1 b) und 7-(Ch1ormethylen)norbornen (1 c) neben den [2 + 21-Cycloaddukten 3b bzw. 3c das zweifache [4 + 21-Addukt 4b bzw. das neuartige Urazol5c (Hauptprodukt) gebildet. 'H-NMR-Spektroskopie (NOE) ergab die Stereochemie der Cycloaddukte 3b,c und 4b, wahrend eine Rontgenstrukturanalyse notwendig war, um das ungewohnliche Umlagerungsprodukt 5c aufzuklaren.
Cycloaddition of 4-phenyl-4H-l,2,4-triazole-3,5-dione (PTAD) to 7-methylenenorbornene (la) afforded the rearrangement urazole 2a in ca. 27% yield. Such urazoles can readily be converted into the corresponding azoalkanes via hydrolysisoxidation').
Since we required for our mechanistic studies on the photodenitrogenation of azoalkanes derivatives with (Z,E) stereolabels, we investigated the PTAD cycloaddition of 7-(phenylmethylene) and 7-(ch1oromethylene)norbornenes (1 b and 1 c),