Transannular tautomerism

In case of the transannular tautomerism of 4(5)-hydroxycyclooctanones (Scheme 5.9) [28], normally the bicyclic tautomer 13b predominates but the portion of the monocyclic tautomer 13a increases with increasing solvent polarity, obviously providing a better solvation of this more polar tautomer [28]. 

Dibenzazepin-2-one, 5-aminomethyl-transannular nucleophilic attack, 7, 25 Dibenzazepin-2-ones tautomerism, 7, 503 Dibenz[6,dJazepinones phenanthridinones from, 2, 507 synthesis, 7, 530 Dibenz[6,d]azepinones, hydrosynthesis, 7, 536 Dibenz[6,eJazepinones synthesis, 7, 529, 530 5H-Dibenz[c,eJazepin-7-ones synthesis, 7, 529... 

An interesting transannular competitive OH- and NH-group addition to the aldehyde C=0 group was observed (86KPS730) for the tautomeric system 53B 53A 53C in CDCI3 solution. 

Scheme 27)48. Irradiation of 111 led to the formation of 112, which was formed by a sequence involving photoaddition and retro-Mannich fragmentation to the intermediate ketoimine, followed by tautomerization of the imine to enamine, transannular closure and dehydration. 

The product from the reaction of chloro-l,3,2-diazaphospholan with a chlorohydrin cyclizes in acetonitrile to give a bicyclic salt (75) which is in a tautomeric equilibrium (see Scheme 5) <77TL1583>. This represents another example of the transannular interactions exhibited by the phosphatranes. 

The absolute configurations of daphmalenines A (20) and B (21) were determined on X-ray diffraction by using the Flack parameter and computational methods, respectively. Daphnioldhamine A (22) is the first Daphniphyllum alkaloid with transannular effect and is easily tautomerized imder acidic or alkaline conditions (Figure 5). 

Reactions of Benzothiazoles with Singlet Oxygen.—Singlet oxygen reacts with 4,5,6,7-tetrahydro-2-methylbenzothiazole in methylene chloride to yield the transannular peroxide (19), which undergoes successive Baeyer-Villiger rearrangement and tautomerism via (20) to the isolable A -acetyl-thio-isoimide... 

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