Tohru Takayasu

Synthesis and spectroscopic properties of azuleno[1,2-g]tricyclo[4.3.1.01,6]deca-5b,7,9-triene derivatives. A nevel cycloheptatriene structure bearing a three carbon bridge at the C1C6 position

Abstract 13-Trifluoroacetyl- and 13-methoxycarbonylazuleno[1,2- g ]tricyclo[4.3.1.0 1,6 ]deca-5b,7,9-trienes were synthesized, and the 13 C NMR spectra revealed that the former exists in a norcaradiene structure, while the latter is in equilibrium between norcaradiene and cycloheptatriene.

On the reaction of azulen-2-ylmethylene(triphenyl)phosphorane. Convenient preparation of azuleno[1,2- f ]- and azuleno[1,2- a ]-azulenes and their properties

Novel azulen-2-ylmethyl(triphenyl)phosphonium bromide has been shown to be a synthon for a rapid new annulation leading to azulenoazulenes. The base treatment of the phosphonium bromide generating azulen-2-ylmethylenephosphorane 9 in situ and subsequent reaction with 5-(dimethylaminomethylene)cyclopenta-1,3-dienecarbaldehyde 10 and 2-chlorotropone 14 affords unsubstituted azuleno[1,2-f]- and azuleno[1,2-a]-azulenes 1 and 2, respectively. The reaction of 9 with 2-chloro-3,5,7-trideuteriotropone has also been carried out to elucidate the reaction paths leading to the formation of 2. The reaction paths involve the Michael-type addition of 9 onto 10 and 14, subsequent proton migration to regenerate the phosphorane moiety, intramolecular condensation of the formyl and carbonyl groups (Wittig reaction) and aromatization. In order to gain insight into the mechanism, PM3 calculations on compounds 9, 10 and 14 as well as on the related compound, (azulen-2-ylimino)tributylphosphorane, have been performed. The reactivity and site-selectivity of the annulation are discussed on the basis of frontier molecular orbital (FMO) theory. The electrophilic aromatic substitution of the azulenoazulenes as well as their spectroscopic and electrochemical properties have also been analyzed.

Umpolung of Tropone: Preparation of 2-Aroyl- and 2-Acyltropones

Abstract The reaction of 2-chlorotropone with DIBAH followed by aldolization with several aldehydes affords 2-(1-hydroxyalkyl)tropones, subsequent oxidation of which results in the formation of 2-aroyl- and 2-acyltropones.

Azulene-annulated tricyclo[4.3.1.01,6]deca-2,4,7-triene derivatives and their anions. A novel cycloheptatriene-norcaradiene valence isomerization in the azulene-annulated tricyclo[4.3.1.01,6]deca-2,4,7-triene ring system

10-Trifluoroacetyl-11,11a-dihydro-4aH-4a,11a-methanoindeno[1,2-a]azulene 18 and methyl {11,11a-dihydro-4aH-4a,11a-methanoindeno[1,2-a]azulen-10-yl}carboxylate 19 are synthesized starting from the azulene-annulation reaction of 2H-cyclohepta[b]furan-2-one with the pyrrolidine enamine derived from tricyclo[4.3.1.01,6]dec-3-en-8-one. The 13C NMR spectra at various temperatures reveal that compound 18 exists in a norcaradiene structure, while compound 19 is in equilibrium between norcaradiene and cycloheptatriene structures. The latter compound is the first example of a cycloheptatriene, which experiences a forced shortening of the C6–C11 distance by a three carbon chain.† The facile valence isomerization of compound 19 is ascribed to the interaction of the lowest unoccupied molecular orbital (LUMO) of the Walsh orbital of cyclopropane and the highest occupied molecular orbital (HOMO) of the methoxycarbonylazulene, and the interaction occurs effectively as to weaken the basal C6–C11 bond of the cyclopropane ring, as compared to that in compound 18 involving an azulene nucleus bearing the more electron-withdrawing trifluoroacetyl group. The hydrogen–deuterium exchange reaction of compounds 18 and 19 in MeONa–MeOD occurs stereospecifically to give 12-exo-deuterated products (exo to the bridge methylene), respectively. Marked spectroscopic differences between the anions 30 and 31, which are derived from compounds 18 and 19 by treatment with [2H5]dimsyl sodium in [2H6]DMSO, respectively, are also observed: the anionic charge in the former is not delocalized over the trifluoroacetylazulene nucleus, while that in the latter is delocalized over the methoxycarbonylazulene nucleus. The thermal rearrangement of the anion generated from compound 19 is also observed to result in the formation of 11-methoxycarbonylazuleno[1,2-a]azulene. Furthermore, the Diels–Alder reaction of the tricyclo[4.3.1.01,6]deca-2,4,7-triene (methanoindeno[1,2-a]azulene) ring system in compounds 18 and 19 has been studied as well.

On the reaction of prop-2-enylidenetriphenylphosphorane derivatives.Novel synthesis of the azulene ring system

Reaction of prop-2-enylidenetriphenylphosphorane derivatives with several tropones has been studied in an attempt to provide a short new route to the azulene ring system. (2-Ethoxyprop-2-enylidene)triphenylphosphorane 4 reacts with 2-chloro-, 2-methoxy- and 2,3,5,7-tetrachlorotropones 7a–c to give azulene derivatives 8 and 9 in moderate yields. On the other hand, reaction of [2-ethoxy-3-(ethoxycarbonyl)prop-2-enylidene]triphenylphosphorane 6 with tropones 7a,c results in the formation of azulene esters 10 and 11 in low yields, whilst that with tropone 7b gives no azulene and substrate 7b is recovered. In order to gain insight into the mechanistic pathways, reaction of phosphoranes 4 and 6 with deuteriated tropones 14a,b which are the corresponding trideuteriated derivatives of compounds 7a,b, have also been studied. Furthermore, compound 4 reacts also with 5-(dimethylaminomethylene)cyclopenta-1,3-dienecarbaldehyde 33 to give 6-ethoxyazulene 37 in moderate yield.

On the reaction of prop-2-enylidenetriphenylphosphorane derivatives. Novel synthesis of 4,9-methanocyclopentacycloundecene derivatives and their spectroscopic and chemical properties

Novel 3-ethoxycarbonyl-2-ethoxy- and 2-ethoxy-4,9-methanocyclopentacycloundecenes 12 and 13 are synthesized by the reaction of 9-chloro-1,6-methano[11]annulen-8-one 8, a 10π-electron vinylogue of 2-chlorotropone, with 2-ethoxy-3-(ethoxycarbonyl)prop-2-enylidene- and 2-ethoxyprop-2-enylidenetriphenylphosphorane, 7a and 7b, respectively. The reaction pathways involve a Michael-type addition of phosphoranes 7a,b onto ketone 8, subsequent proton migration regenerating the phosphorane moiety, which undergoes intramolecular Wittig reaction, and aromatization, eliminating HCl. The 1H NMR spectra show that compounds 12 and 13 are aromatic molecules having a diatropic 14-electron cyclic π system. The UV–visible absorption spectra of compounds 12 and 13 exhibit extended cyclic conjugation of the aromatic perimeter according to a bathochromic shift of the longest absorption maxima as compared to those of the related azulene derivatives having the same substituents. In addition, the first example of an aromatic substitution reaction of the methanocyclopentacycloundecene ring system has been studied, and shows that the compounds 12 and 13, like azulene, undergo trifluoroacetylation under exceptionally mild conditions and exhibit the same site-selectivity as does azulene. The electrochemical properties of compounds 12 and 13 as well as the related azulene derivatives are also analyzed and discussed on the basis of MNDO calculations.

On the reactions of (vinylimino)phosphoranes and related compounds. Part 30. Short new synthesis of 5-azaazulene derivatives. Some comments on reactivities of (vinylimino)phosphoranes

A short new synthesis of phenyl-substituted and annulated 5-azaazulene (cyclopenta[c]azepine) derivatives 15–18 consists of the reaction of [(1-phenylvinyl)imino]- and benz-annulated [(cycloalkenyl)imino]-phosphoranes 8–11 with 5-(dimethylaminomethylene)cyclopenta-1,3-dienecarbaldehyde 1 in an enamine alkylation (Michael addition) process, subsequent proton migration–ketonization, and condensation of the formyl group with the iminophosphorane moiety (aza-Wittig reaction). On the other hand, reactions of aldehyde 1 with (vinylimino)phosphoranes12–14, which have no phenyl group at the α-position relative to the nitrogen atom, consist of a intramolecular aza-Wittig reaction or a substitution reaction of aldehyde 1 with phosphoranes 12–14 and subsequent hydrolysis to afford 5-(aminomethylene)cyclopenta-1,3-dienecarbaldehyde 19 and its derivatives 20 and 21, respectively. In the context of selectivity observed in the reaction of phosphoranes 8–11 and 12–14 with aldehyde 1, respectively, MNDO calculations on compounds 1 and 12A, 12B as well as on model compounds 8C–12C were performed to gain insight via a theoretical interpretation based upon frontier molecular orbital theory (FMO): the former reaction, giving 5-azaazulene derivatives, would be an FMO-controlIed reaction, while the latter is a charge-controlled reaction. Several spectral and chemical properties of heterocycles of 16–18 are analysed.