135127-41-2Relevant academic research and scientific papers
Nucleophilic Singlet Carbenes in the Cycloaddition with 1,2,4,5-Tetrazines: a New Synthesis of Isopyrazoles
Gerninghaus, Christian,Kuemmell, Andreas,Seitz, Gunther
, p. 733 - 738 (2007/10/02)
A series of 3,6-disubstituted 1,2,4,5-tetrazines 6, including C6H5, SCH3, SO2CH3, N(CH3)2, CF3, CO2CH3 groups, has been submitted to cycloaddition with the nucleophilic singlet carbenes 4, 15, and 20, which are generated from the precursors 1, 11 and 19, resp.In all cases isopyrazoles (4H-pyrazoles) 9, 10, 18, and 21 are isolated in good yields.They are formed in a two-step reaction sequence with the cycloadducts of type 8 as intermediates which eliminate nitrogen by subsequent cycloreversion.The acceptor-substituted isopyrazole 9e is characterized as an electron-deficient diene by some Diels-Alder reactions with inverse electron demand leading to the expected azo-bridged cycloadducts 23, 25, 27, 29, and 31 without acid catalysis or aplication of higher pressure.With cyclooctyne (32), the cycloaddition is followed by a cycloreversion with formation of the cyclopentacyclooctene 34.Key Words: Singlet Carbenes / Cycloadditions / Isopyrazoles / Diels-Alder reactions / Cycloreversion
Nucleophile singulett-carbene in der inversen [4+]-cycloaddition: Eine neue isopyrazol-synthese
Kuemmeil, Andreas,Seitz, Guenther
, p. 2743 - 2746 (2007/10/02)
Dimethoxycarbene, generated from the norbornadienone ketal 6 or from triethyl orthoformate 12a can be trapped by various 1,2,4,5-tetrazines 1 to yield the corresponding isopyrazoles 10 in high yields via [4+1]-cycloaddition followed by [4+2]-cycloreversio
