ISSN:
0170-2041
Keywords:
6H-1,2-Oxazines
;
Methoxyallene
;
Nitroso alkene
;
Hetero Diels-Alder reaction
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Regioselective hetero Diels-Alder reactions of in-situ generated nitroso alkenes 2-4 with methoxyallene derivatives 1 provide 4H-1,2-oxazines 5-7 with an exo-methylene group at C-5. These primary cycloadducts are smoothly transformed into conjugated 6H-1,2-oxazines 11-13 by base or acid catalysis. The bicylic nitroso alkene 17 and methoxyallene (1a) combine to give the tricyclic 1,2-oxazine 18, thus demonstrating that an exo-transition state is favoured in this [4+2] cycloaddition. The reaction of the sterically hindered methoxyallene 1h with nitrosostyrene affords the cycloadduct 22 in low yield. 22 is very likely formed by a two-step Diels-Alder reaction via a zwitterion. Allene derivatives lacking a methoxy group are not sufficiently reactive towards nitroso alkenes and do not provide 1,2-oxazines.
Additional Material:
8 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.1991199101101
Permalink
