On the Intramolecular 1,4-Dipolar Cycloaddition Reaction of Thiazinium Betaines for the Construction of Aza-, Diaza-, and Polyaza HeterocyclicRing Systems
δείτε την πρωτότυπη σελίδα τεκμηρίου στον ιστότοπο του αποθετηρίου του φορέα για περισσότερες πληροφορίες και για να δείτε όλα τα ψηφιακά αρχεία του τεκμηρίου*
On the Intramolecular 1,4-Dipolar Cycloaddition Reaction of Thiazinium Betaines for the Construction of Aza-, Diaza-, and Polyaza HeterocyclicRing Systems
(EN)
Padwa, A.;
(EN)
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
(EL)
Padwa, A.;
(EN)
A series of bicyclic anhydro-4-hydroxy-2-oxo-1,3-thiazinium hydroxides containing tethered Ο€-systems are easily prepared from the reaction of thiolactams with 1,3-bielectrophiles. These cross-conjugated heteroaromatic betaines undergo regio- and stereospecific 1,4-dipolar cycloaddition in good yield to produce cycloadducts containing a carbonyl sulfide bridge which can be induced to lose COS on further heating. Two of the cycloadducts were characterized by single crystal X-ray determinations. Control of ring size in the final product of the cycloaddition can be achieved by variation of the dipolarophilic chain length. Entry to the [6,6,5]- and [6,6,6]pyridone ring systems was possible using phenylalkynyl-substituted thioamides. Intramolecular 1,4-dipolar cycloaddition of a thiazinium betaine dipole also occurs across an indolyl Ο€-bond. With only one substituent group in the 9-position of the bicyclic betaine, the reaction takes an entirely different course unless a highly activated Ο€-bond is incorporated into the tether. The preferred reaction with modestly activated Ο€-systems corresponds to loss of the activated proton to produce an S,N-ketene acetal. When a ketene S,S-acetal group was incorporated onto the side chain, the 1,4-dipolar cycloaddition reaction was facilitated relative to proton loss.
(EN)
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