4- Azaazulenes cycloadditions

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). 

Wittig reactions with pyrrole-2-aldehyde led to the esters (79) which were cyclisized to 3a-azaazulen-4-ones (80).104,105 4-Methylene-3a-aza-azulenes (81) have been obtained from 80 with stabilized phos-phoranes.36 Reaction of dimethyl acetylenedicarboxylate with 81 could not be achieved. A similar cycloaddition was successful in the synthesis of cycl[3,3,3]azines (2) (Section V). 

Cycloaddition reactions have been carried out with corresponding bases of Vilsmeier salts of pyrroles. Thus reaction of 153 with dimethyl acetylenedicar-boxylate gave pyrrolizines 154 and 3a-azaazulenes 155 in a nonsynchronous reaction. The structure of 3H-pyrrolizine 154a was proved by X-ray analysis.96 In a closely related reaction, pyrrolizinones 156 and 157 were obtained from the corresponding Vilsmeier salts with phenyl isocyanate.97 Reaction of 2-p-nitrobenzoylindolin-3-one (158) with methyl acetoacetate gave the benzopyrrolizinone (159).5 7... 

Cycloaddition reactions have been carried out with Vilsmeier bases of pyrroles. Thus reaction of (180) with dimethylacetylene dicarboxylate gave pyrrolizines (181) and 3a-azaazulenes (182) in a non-concerted reaction <74JHC811>. In a closely related reaction, (183) was obtained from the Vilsmeier base with phenyl isocyanate <76H(4)i28i>. 

In another cycloaddition, 2-acylamino-3-ethoxycarbonyl-l-azaazulene (196) reacts with DMAD in refluxing MeCN to produce the diazapentaleno[l,6-a/lazaazulene-l,2,2a,3,5-pentacarboxylate ester (197) <92BCJ1784>. 

Azaazulenes are versatile precursors in syntheses of peri-fused azulenopyrrole derivatives in the course of the [8+2] cycloaddition by means of electron-deficient acetylenes or of acetylene equivalents (Schemes 45 and 46). Treatment of l-aza-2-azulenones 196a and 196b... 

Synthesis of Heterocycles. TMSK has also gained prominence as a useful reagent for accessing various heterocycles. TMSK reacts readily with aA -diarylnitrones to afford N-alkyloxindoles, which can subsequently be converted to oxindoles upon hydrolysis (eq 19). The analogous ring expanded 3,3a-dihydro-3-trimethylsilyl-l-azaazulen-2(lH)-ones can also be accessed via an [8 + 2] cycloaddition of TMSK with 8-azahepta-fulvenes.4 ... 

The [8+2] cycloaddition reaction of 8-azaheptafulvenes 500 with 2-chloroketenes constitutes an efficient synthetic method for the preparation of azaazulen-2-ones 501 (Scheme 6.132a) [297, 298]. The reaction with aryl... 

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