ISSN:
0947-3440
Schlagwort(e):
4H-Pyrazole synthesis
;
Dimethoxycarbene
;
Diels-Alder reactions, „inverse“
;
Isopyrazolium ketal cations
;
Phthalazinecarboxylates
;
Chemistry
;
Organic Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
3,6-Diphenyl-1,2,4,5-tetrazine (6) reacts with dimethoxycarbene (7), generated from the 1,3,4-oxadiazoline 8, to yield the 4H-pyrazole 10. This is alkylated to the N-methyl-4H-pyrazolium tetrafluoroborate 12 in high yield. The alkylated, cationic azine system of 12 serves as electron-deficient diene in a [4+ + 2] cycloaddition with inverse electron demand and reacts diastereoselectively with several cyclic olefins as electron-rich dienophiles. The initially formed cationic [4+ + 2] adduct, e.g. 15, is unstable and rearranges probably via 16 to a racemic phthalazinecarboxylic ester of type 17. The crystal structures of the epoxyphthalazinecarboxylic ester 25 and of the trans-annulated cycloocta[d]pyridazine 27 were determined by X-ray diffraction. In contrast to the cyclic olefins, cyclooctyne (28) reacts with the pyrazolium cation 12 to yield the cyclooctapyridiazinium tetrafluoroborate 30 via the cycloadduct 29.
Zusätzliches Material:
2 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/jlac.1995199507174
Permalink
