4- Azaazulenes oxidation

Pyrrolotropone is formed by a thermal retro-Grignard reaction from a 4-aryl-4-hydroxycyclohepta[i]pyrrole derivative (72CB1224). Finally, cycloadditions of 8-styryl-l-azaazulenes with dimethyl acetylenedicarboxy-late and subsequent oxidation yield 1,7-ansa-bridged pyrrolotropones (80BCJ1406). 

Cycloheptapyrrolotropones 645 and 646 (see Scheme 173) are obtained, along with azaazulene 644, on oxidizing dihydro derivative 642 [94JCS(P1)2579]. 

Apart from investigations of the mechanism of the Clemmensen reaction ensuing from the formation of 3, work on the reactivity of nitrenes (Section IV,A,4), as well as studies of photochemical rearrangements of acridine Af-oxides (Section IV,B), have led to 4-azaazulenes. 

Treatment of perhydro-4-azaazulene (3) with mercuric acetate produces a mixture of dehydro derivatives 31a and 31b, which, with acids, yields homogeneous salts of structure 32 (56JOC344). The enamine 34, which was obtained by the same route from 33, served as a model compound in a study of the synthesis of cephalotaxine (72JOC3691). A reaction with ethyl y-bromo-acetoacetate surprisingly yielded the quinolizidine 36, which was formed by rearrangement of the intermediate annellation product 35 (Scheme 3) Phthalimides 38 were obtained from a Baeyer-Villiger oxidation of 4-azaazulen-3-ones 37 (77JOC1093). 

From a Polonowski reaction of narceine imide Af-oxide 73b N-bridgehead bicycles 75 were obtained containing functional groups in the 5-position. Reaction of 75 (R = OAc) with ethanolic sulfonic acid gave 75 (R = OC2H5), together with the azaazulen-3-one derivative 76 (82MI1). 

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