Photochemistry of Aminoketones. V. Diastereoselective Synthesis of 3‐Aryl‐azetidin‐3‐ols via Photocyclization of Aryl‐α‐amidoalkyl‐ketones
N‐Acyl‐azetidin‐3‐ols 3 and 4 are formed by diastereoselective cyclization of n,π*‐excited N‐benzyl‐N‐phenacyl‐amides 1 and 2 in ether solution. Dependent on the nature of the p‐and α‐substituents of the phenacyl part and especially of the N‐acylgroups in the amides 1 and 2 competing reactions occur, particularly the NORRISH II cleavage and an oxydative cleavage of the intermediate hydroxybiradicals A. N‐Acylgroups with low energy barrier ΔG≠ of internal rotation favour the diastereoselective photocyclization by intramolecular interaction between the amide oxygen atom and the n,π*‐CO‐group in 1*, 2* and the OH group in the biradicals A, respectively. An intramolecular hydrogen bonding enables the N‐tosyl‐azetidinols 3 to rearrange to the N‐tosylamino‐methyl‐benzhydryl‐ketones 6 by 1‐sensitized photoreaction.
Es wird untersucht, ob und in welchem Umfang Mannichbasen des Tetralons‐(1), 3,3,6,8‐Tetramethyltetralons‐(1), Acenaphthenons, 4‐Chromanons und des N‐Methylpiperidons‐(4) bei der Amineliminierung durch Acetolyse, über die monomeren, α,β‐ungesättigten Methylenketone nach Art einer Diensynthese in Dihydropyrane übergehen. Die Ergebnisse werden mit früheren Untersuchungen an Mannichbasen cyclischer Ketone verglichen.
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