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Molecules 2001, 6(4), 353-369; doi:10.3390/60400353
Article

π-Bond Screening in Benzonorbornadienes: The Role of 7-Substituents in Governing the Facial Selectivity for the Diels-Alder Reaction of Benzonorbornadienes with 3,6-Di(2-pyridyl)-s-Tetrazine

*  and
Received: 3 November 2000; Accepted: 6 November 2000 / Published: 31 March 2001
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Abstract: Benzonorbornadiene 21, 7-spirocyclopropylbenzonorbornadiene 23, 7,7-dimethylbenzonorbornadiene 25, and 7-spirocyclopentylbenzonorbornadiene 27 have been reacted with 3,6-di(2-pyridyl)-s-tetrazine (rate: 21>23>25=27) to form symmetrical 4,5-dihydropyridazines which are stable towards fragmentation but rearrange with varying facility to their 1,4 isomers. The facial selectivity of attack on the π-bond changes from exo-attack for 21 and 23 to endo-attack for 25 and 27. The 7-spirocyclopropyl benzonorbornadiene 23 typically forms a mixture of dihydropyridazines with exo-stereochemistry, which undergo further stereochemical isomerisation to an exo-fused product upon acetylation (acetyl chloride in hot pyridine). Oxidation with DDQ of the dihydropyridazines individually or as mixtures gives the corresponding fused 3,6-di(2-pyridyl)pyridazines.
Keywords: 3; 6-di(2-pyridyl)-s-tetrazine; cycloaddition; steric effects; endo-addition; di(2- pyridyl)pyridazines 3; 6-di(2-pyridyl)-s-tetrazine; cycloaddition; steric effects; endo-addition; di(2- pyridyl)pyridazines
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Warrener, R.N.; Harrison, P.A. π-Bond Screening in Benzonorbornadienes: The Role of 7-Substituents in Governing the Facial Selectivity for the Diels-Alder Reaction of Benzonorbornadienes with 3,6-Di(2-pyridyl)-s-Tetrazine. Molecules 2001, 6, 353-369.

AMA Style

Warrener RN, Harrison PA. π-Bond Screening in Benzonorbornadienes: The Role of 7-Substituents in Governing the Facial Selectivity for the Diels-Alder Reaction of Benzonorbornadienes with 3,6-Di(2-pyridyl)-s-Tetrazine. Molecules. 2001; 6(4):353-369.

Chicago/Turabian Style

Warrener, Ronald N.; Harrison, Peter A. 2001. "π-Bond Screening in Benzonorbornadienes: The Role of 7-Substituents in Governing the Facial Selectivity for the Diels-Alder Reaction of Benzonorbornadienes with 3,6-Di(2-pyridyl)-s-Tetrazine." Molecules 6, no. 4: 353-369.


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