An efficient preparation and spectroscopic and electrochemical properties of quinodimethane derivatives with four 3-(methoxycarbonyl)azulen-1-yl groups

Reaction of methyl 1-azulenecarboxylate (8) with terephthalaldehyde (9) in acetic acid in the presence of hydrochloric acid at 25 °C for 2 h gives 1,4-bis[bis(3-methoxycarbonyl-1-azulenyl)methyl]benzene (12), in 93% yield, which upon oxidation with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in dichloromethane in the presence of hexafluorophosphoric acid at 25 °C for 1 h affords the dicarbenium-ion compound 15 in 94% yield. Furthermore, reduction of 15 with zinc powder in a mixed solvent of acetonitrile and chloroform at 25 °C for 1 h yields the target quinodimethane 18 in 90% yield. Similarly, as in the case of 18, the quinoid compounds 19 and 20 can be derived from the dicarbenium-ion compounds 16 and 17, quantitatively. A facile preparation as well as spectroscopic and electrochemical properties of 15-20 is reported.     

Reactions of guaiazulene with thiophene-2,5-dicarbaldehyde and furan-2,5-dicarbaldehyde in methanol in the presence of hexafluorophosphoric acid: a facile preparation and properties of delocalized dicarbenium-ion compounds stabilized by two 3-guaiazulenyl groups and a thiophene (or furan) ring

Reaction of guaiazulene (1) with thiophene-2,5-dicarbaldehyde (2) in methanol in the presence of hexafluorophosphoric acid at 25 °C for 3 h gives as high as 90% isolated yield of the delocalized dicarbenium-ion compound, 2,5-thienylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (3). Similarly, reaction of 1 with furan-2,5-dicarbaldehyde (4) under the same conditions as the above reaction affords the corresponding dicarbenium-ion compound, 2,5-furylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (5), in 84% isolated yield. Along with a facile preparation and the spectroscopic and electrochemical properties of 3 and 5, comparative studies on the ¹H and ¹³C NMR spectral and chemical properties of 3 and 5 with those of the delocalized mono- and dicarbenium-ion compounds [i.e., (3-guaiazulenyl)(2-thienyl)methylium hexafluorophosphate (7), (2-furyl)(3-guaiazulenyl)methylium hexafluorophosphate (9), α,α′-bis(3-guaiazulenylmethylium) bis(tetrafluoroborate) (10), 1,2-phenylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (11), and 1,4-phenylenebis(3-guaiazulenylmethylium) bis(tetrafluoroborate) (12)] are reported. Moreover, referring to the results of the X-ray crystallographic analyses of 7, 9, 11, and 12, the optimized 2,5-thienylenebis(3-guaiazulenylmethylium)- and 2,5-furylenebis(3-guaiazulenylmethylium)-ion structures for 3 and 5, calculated by a WinMOPAC (version 3.0) program using PM3 as a semiempirical Hamiltonian, are described.