A NITROGEN ANALOG OF SESQUIFULVALENE¹

Cyclopenta[a]quinolizine: A Novel Pseudoazulene with a Bridgehead Nitrogen Atom

“…Because the five-membered ring has a major contribution to the HOMO of 4 and the terminal pyridine ring has a major contribution to its LUMO (Figure 3), it seems reasonable to assign the shoulder appearing at long wavelength in the spectra of 4 to the transition from the HOMO to the LUMO. However, the quantitative picture is not so straightforward, and the calculated HOMO-LUMO gap, as in the case of azulene, [23] does not correspond numerically to the observed band that is responsible for the color of 4. The best theoretical simulation of the experimentally observed UV/Vis spectra of 4 was achieved (see vertical lines in Figure 2) by DFT calculation involving at least six excited states.…”

“…The spectra of 4 (Figure 2), which are different from those of 1b by an additional broad maxima at 350-420 nm, strongly resemble the spectra of pyridofulvene 6 (with red-orange color and two broad maxima at λ = 360-400 and 450-560). [23] Therefore, the color of 4, similarly to 6, is probably linked to charge transfer from the five-to six-membered terminal ring (cf. dipolar structure C in Scheme 5).…”

Fulvenes and substituted fulvenes

“…Nitrogen and sulfur analogs of compounds such as XI and XII are accessible by a number of routes: cyclopentadienylsodium gives with 4-bromo-N-benzylpyridinium bromide l-benzyl-4-cyclopentadienylidene-1,4-dihydropyridine (XXII) (47) and with 2-bromo-Nmethylpyridinium bromide the analog XXIII (48). Likewise, 4-alkoxyor -aryloxypyridinium salts react with cyclopentadiene in the presence of potassium Z-butoxide (69).…”

“…Likewise, 4-alkoxyor -aryloxypyridinium salts react with cyclopentadiene in the presence of potassium Z-butoxide (69). Also 9-(4-pyridyl) fluorenol (XXIV) can be transformed by alkylation plus dehydration and oxidation into compounds of type XXV (47).…”