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- Title
Photochemisches Verhalten von 1- und 2-alkylierten 1, 2-Dihydronaphthalinen bei tiefen Temperaturen.
- Authors
Sieber, W.; Heimgartner, H.; Hansen, H.-J.; Schmid, H.
- Abstract
The irradiations of 1, 1-dimethyl- (8), 1, 1-di-(tri-deuteriomethyl)- (d6- 8), 1, 1, 2, 2-tetramethyl- ( 9) and cis- and trans-1, 2-dimethyl-1, 2-dihydronaphthalenes ( cis- and trans- 10) were investigated in 2, 2-dimethylbutane/pentane at −100° using a mercury high-pressure lamp, and with mercury high- and low-pressure lamps at room temperature. The results were compared with one another, and those of the individual compounds are collected in schemes 2 and 4-7. The most important results are the following: 1. The 1, 2-dihydronaphthalenes undergo a conrotatory ring opening to the o-quinodimethanes on irradiation with high- or low-pressure lamps at room temperature or at −100°. Thermal reactions ([1, 7a]H-shifts, electrocyclisations) are suppressed at −100°. The o-quinodimethanes formed from 8 (scheme 2), 9 (scheme 5) or cis- 10 (scheme 6) undergo on irradiation with the high-pressure lamp, [1, 5]H-shifts or photochemical Diels-Alder reactions after renewed photochemical excitation, to yield the benzobicyclo[3.1.0]hex-2-ene derivatives. These Diels-Alder reactions do not proceed stereospecifically, and therefore are not orbital symmetry controlled reactions. 2. If the 1, 2-dihydronaphthalenes are irradiated at room temperature with either a high- or a low-pressure lamp, then the initially formed o-quinodimethanes undergo thermal [1, 7a]H-shifts, in preference to all other reactions, as long as this is sterically possible; the resulting products can undergo secondary photochemical transformations. Such o-quinodimethanes are formed on irradiation of 8, 9 and cis- 10. From trans- 10, an o-quinodimethane mixture is formed, of which one component ( cis, cis- 22) undergoes thermal [1, 7 a] H-shifts, while the other ( trans, trans- 22) suffers a thermal disrotatory electrocyclisation to give cis- 10. If a high-pressure lamp is used in the last experiment, then the competing photochemical Diels-Alder cyclisation to bicyclic compounds of the type 23 (scheme 7) can result in the trans, trans- 22. As was shown by Salisbury [3], and confirmed by ourselves in other cases [2], photochemical Diels-Alder reactions or [1, 5] H-shifts in the o-quinodimethanes require light of wavelength ⩾ 400 nm (high-pressure lamp). The present photochemical investigations amplify and confirm our earlier conclusions concerning the photochemistry of the 1, 2-dihydronaphthalenes [2].
- Publication
Helvetica Chimica Acta, 1972, Vol 55, Issue 8, p3005
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/hlca.19720550833