Azulenes with aldehydes

The pKa values given for diphenylcyclopropenone, tropone and azulene-l-aldehyde were obtained by spectrophotometric titration with aqueous acids in the author s laboratory these figures are accurate to 0.3 pK units. The dipole moment of perinaphthenone in benzene was measured by R. J. Best and K. Mead of the Stamford laboratories of the American Cyanamid Co., Connecticut, U.S.A. 

The condensation of a vinylogous formamide with an enamine has been applied to an aza azulene synthesis (351). The point of attachment of the aldehyde to the enamine in condensations with indolenin derived poly-enamines was found to favor the second double bond (352,353). 

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). 

The reactivity of these methyl groups is normally enhanced by nitrogen atom quaternization. Benzotroponopyridinium salt 505 with two molecules of azulene aldehyde condenses to afford blue-black bis(azulenylvinyl) dye 506 (Amax 536 nm 62ZC369). Furthermore, oxazolium salt 507 condenses with activated benzothiazolium salt 508 (Scheme 134) to form unsymmetri-cal trimethine cyanine 509 (63UP1). (Dyes 512a,b arise from methylthio exchange Section IV,A,5,e.)... 

Photocleavage of benzyl-S bonds appears to proceed neither by an electron transfer pathway nor with participation of an exciplex. A meta effect seems to operate in these reactions as evidenced by the influence of 3-methoxy and of 3-cyano substituents on the efficiency of the cleavage process. Photolysis of 1,2-bis(phenoxymethyl)-, l,2-bis(phenylthiomethyl)-, and l,2-bis(phenylseleno-methyl)benzene induces a two-photon process to give o-quinonedimethane, which in the presence of dienophiles undergoes a cycloaddition reaction, and 4,8,10-trithiadibenzo[cd,ij]azulene 8-oxides gives the corresponding aldehydes and ketones together with 4,8,9-trithiacyclopenta[def]phenanthrene. The two... 

Rigby synthesized a [5.3.1] oxa-bridged nucleus in the context of a perhydro-azulene synthesis [89]. Upon treatment of 81 with BF3 etherate, a hetero-Diels-Alder reaction between the aldehyde and the diene occurred to give 82 in good yield, Eq. 62. 

Azulenes undergo condensation reaations with aryl and heteroaryl aldehydes in the presence of mineral acids to give azulenium salts, which can react with nucleophiles to give a variety of 1-substituted derivatives, e.g. [82,125,128,129]. 

By replacing 105 with aromatic aldehydes 69 in this three-component domino reaction, a total of 38 examples of benzo[f]azulen-l-ones 164 in good overall yields (70-89%) have been synthesized with high regioselectivity (Scheme 12.66) [90]. 

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