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Photochemische Reaktionen 49. Mitteilung [1] Spezifisch π → π*‐induzierte Keton‐Photoreaktionen: Die Doppelbindungsverschiebung von O‐Acetyl‐10α‐testosteron Protonisierung der Doppelbindung seines δ 5 ‐Isomeren
Author(s) -
Kuwata S.,
Schaffner K.
Publication year - 1969
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19690520118
Subject(s) - chemistry , ketone , double bond , enone , photochemistry , intramolecular force , excited state , stereochemistry , organic chemistry , physics , nuclear physics
The α,β‐unsatured ketone 10α‐testosterone has been reported previously [6] to photoisomerize in t ‐butanol solution to the β,γ‐unsaturated ketone. The irradiation had been carried out using a high‐pressure mercury lamp in a quartz vessel. For structural reasons this double bond shift cannot proceed through a photoenolization mechanism involving an intramolecular hydrogen transfer from the γ‐position to the enone oxygen as has been suggested to operate in several formally analogous cases of aliphatic enone isomerizations. In the present reinvestigation, O‐acetyl 10α‐testosterone ( 1 ) was used, employing selectively either excitation of its n → π* (with wavelengths > 300 nm) or its π → π* absorption band (with 253,7 nm). In t ‐butanol solution the doublebond shift 1 → 2 could be effected with π→* excitation only. Experiments in deuterated solvent ( t ‐BuOD) resulted in deuterium in corporation in both the δ5‐ketone in the C(4)‐position, cf.( 3 ) and in the conjugated ketone. These results indicate that the reactions is initiated either in the, S π,π* state or in a high vibrational mode of the S 0 or t ππ* state. n → π* Excitation of 1 in t ‐butanol gave essentially no over‐all chemical change, while in benzene solution it resulted again in a double bond isomerization ( 1 → 2 ). In analogy to results with similar enones [28] under identical conditions the deconjugation in benzene may be the consequence of an intermolecular hydrogen abstraction of the T n ,π* excited state of the enone. Another specifically π →π* induced photoreaction was observed on irradiation of the β, γ‐unsaturated ketone 2 in t ‐BuOD with 253,7 nm. The olefinic hydrogen at C‐6 of 2 was exchanged with deuterium and, to a small extent, isomerization to the conjugated ketone 1 with concomitant deuterium incorporation occurred. It is concluded that from the higher excited state of the β, γ‐unsaturated ketone, but not from its S n ,π* state, an activation mode of the double bond is accessible to effect D+ addition at C‐6 followed by deprotonation to 4 and to deuterated 1 , respectively.