The condensation product of 2‐aminophenol and glyoxal. Structure and photochemistry

Abstract

It has been shown by X-ray analysis that the condensation product of 2-aminophenol and glyoxal is 5a,6,11a,12-tetrahydro[1,4]benzoxazino[3,2-h][1,4]benzoxazine (5) and not, as generally assumed'), 2,2'-bibenzoxazoline (4). The structure of 5 is preserved if it is dissolved in neutral solvents. Thermal oxidation of 5 leads preferentially to the formation of bibenzoxazole 7 and only with small yields to benzoxazinobenzoxazine 8. The photooxidation reaction of 5 is wavelength dependent. Long wavelength excitation yields exclusively 7, short wavelength excitation yields also 7, but in addition 8. The photooxidation 5+7 requires two photons: The first product is the metastable dihydrobibenzoxazole 10 which is converted by a second photon into 7. The photooxidation 5 -4 3 is presumably a one-photon process. Struktur und Photochemie eines Kondensationsproduktes aus ZAminophenol und GlyoxalMit Hilfe der Rontgen-Strukturanalyse konnte gezeigt werden, daB bei der Kondensation Bei kurzwelliger Anregung entsteht ebenfalls 7, daneben jedoch auch 8. Zur Photooxidation 5+7 sind zwei Photonen erforderlich. Zunachst bildet sich das metastabile Dihydrobibenzoxazol 10, aus dem nach der Absorption eines zweiten Photons 7 entsteht. Die Photooxidation 5-8 ist wahrscheinlich ein Ein-Quanten-ProzeB. The Structure of the Condensation ProductFor the condensation product (CP) of 2-aminophenol (1) and glyoxal (2) the structures 3 to 6 are conceivable (Scheme 1). Since CP forms chelates with a number of divalent cations (e.g. Cu2@, Mg2@, Ca2@), Bayer') first assumed that the Schiff base 3 is the chelating reagent. CP is commercially available (Fluka)

The standard molar enthalpies of combustion and sublimation of benzothiazino-benzothiazine and benzoxazino-benzoxazine

“…The synthesis and molecular structure of the cis-5a, 6,11a,12-tetrahydro [1,4]benzothiazino [3,2-b] [1,4]benzothiazine (BTB) (figure 1) and for 5a,6,11a,12-tetrahydro [1,4]-benzoxazino [3,2-b] [1,4]benzoxazine (BOB) (figure 1) were reported by Farfa´n et al (1) and by Tauer et al (2) From here on, these compounds will be a To whom correspondence should be addressed.…”

“…The compound BTB was prepared by the method described by Farfa´n et al (1) and was purified by crystallization from diethyl ether, and BOB was prepared by the method described by Tauer et al, (2) and purified by crystallization from ethanol. The samples were dried overnight at the temperature T = 338 K in a vacuum oven in order to eliminate solvent trapped during crystallization.…”

Fused heterocycles derived from pseudoephedrine and ephedrine

“…The reaction of pseudoephedrine with glyoxal in a 2: 1 ratio was carried out in benzene under reflux for 2 h. The crude reaction product is a mixture of (2R* ,3R* ,6R* ,7R*)-2,6-diphenyl-3, 4 4'R*, 5R*, 5'R*)-5,5'-diphenyl-3,3',4,4'-tetramethyl-2,2'-bioxazolidines, mp 18 1-1 83°C (6) and 1 19-1 21°C (7), which were separated by fractional crystallizations using hexanemethanol mixtures.…”

“…Subsequent studies (4) showed that there were two additional conceivable structures (3a and 4) for the reaction of glyoxal with o-aminophenol. Structure 4 was excluded, based on the 270 MHz 'H nmr spectrum, since for this isomer the '~u t h o r to whom correspondence may be addressed.…”

“…However, since the proton spectrum does not allow a distinction between structures 2 or 3 a , and photochemical experiments did not permit establishing the structure, the condensation product was definitively established as 5a,6,1 l a , 12-tetrahydro-cis-[l,4]-benzoxazino[3,2-b:l[1,4]-benzoxazine (3a) by a single crystal X-ray diffraction study (4). Closely related studies report the reaction of 2-propyn-I01s with 2-aminoalcohols and mercury(I1) chloride (5), the reaction of 2-methylaminoethanol with glyoxal (6), and the reaction of 2-methylaminoethanol with gem-dibromoketones (7), which have been shown to proceed by highly…”