ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Photochemistry of 1,1-dimethyl-4-phenyl-and 1-Methyl-1-phenyl-1,2-dihydronaphthalene; evidence for a photochemical, sigmatropic [1,7]H-shift.Irradiation of 1,1-dimethyl-4-phenyl-1,2-dihydronaphthalene (11) and 1-methyl-1-phenyl-1,2-dihydronaphthalene (8) in pentane were investigated at -112° to -118°, using a mercury high pressure lamp. The [1,5]-hydrogen-shift products 13 and 17, respectively, the [1,7]-hydrogen-shift products 15 and 10, respectively and the photochemical Diels-Alder products 14 and 18, respectively, were obtained, presumably via the ω-vinyl-o-quinodimethane intermediates 12 and 9 (Schema 3).Irradiation of the 1,2-dihydronaphthalene 11 at -181° to -183° in a 2,2-dimethylbutane/pentane matrix, gave rise to an UV.-maximum at 402 nm which is assigned to the o-quinodimethane derivative 12. After warming the solution around -130° or to room temperature, a product mixture was obtained, which mainly consist of the [1,7]-hydrogen-shift product 15 accompanied by the [1,5]-hydrogen-shift products 13 and 16 and the photochemical Diels-Alder product 14 (Table 1). When the o-quinodimethane intermediate 12 was irradiated with 406 nm-light, the longwavelength absorption completely disappeared. This solution, after warmingup, yielded mainly the [1,5]-hydrogen-shift products 13 and 16 together with the bicyclic compound 14 and surprisingly a small amount of the [1,7]-hydrogen-shift product 15 (Table 1).Similar experiments were carried out with the 1,2-dihydronaphthalene 8. The results clearly indicate that irradiation of the o-quinodimethane 9 at -180° to -185° with 406 nm-light caused [1,5]- and [1,7]-hydrogen shifts in a ratio of approximately 1:1 (Table 2).From the experiments described above it follows, that the phenyl-substituted α-methyl-ω-vinyl-o-quinodimethanes 12 and 9 undergo upon irradiation with light of λ 〉 400 nm, besides photochemical Diels-Alder reactions, also [1,5]- and [1,7]- hydrogen shifts.It is remarkable that the thermal [1,7]-hydrogen-shifts of the o-quinodimethanes 12 and 9 occur readily around -130°, whilst a temperature of -70° is needed to promote [1,7]-hydrogen-shifts in the non-phenylated o-quinodimethanes of the type 2 (Schema 1). The phenyl group in ω- or α-position may enter into conjugation with the π-system in the helcal transition state of the [1,7]-hydrogen shift, but not in the reactants 12 and 9.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19750580733
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