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Authors = Ronald N. Warrener

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17 pages, 560 KiB  
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
by Ronald N. Warrener and Peter A. Harrison
Molecules 2001, 6(4), 353-369; https://doi.org/10.3390/60400353 - 31 Mar 2001
Cited by 20 | Viewed by 11016
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 [...] Read more.
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. Full article
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9 pages, 55 KiB  
Article
7-(1-Acetoxymethylidene)Benzonorbornadiene: A Versatile Reagent for the Synthesis of 7-Formyl and 7-Hydroxymethyl Benzonorbornadienes
by Ronald N. Warrener, Geoffrey J. Collin and Patrick J. Foley
Molecules 2001, 6(3), 194-202; https://doi.org/10.3390/60300194 - 28 Feb 2001
Cited by 4 | Viewed by 6973
Abstract
7-(1-Acetoxymethylidene)benzonorbornadiene 3, prepared in one step by the addition of benzyne to 6-acetoxyfulvene 2, is hydrolysed in acid solution to form a 3:2-epimeric mixture of syn- and anti- 7-formylbenzonorbornadienes 4 and 5, respectively; the corresponding 7-hydroxymethylbenzonorbornadienes 6 and 9 were produced by reduction [...] Read more.
7-(1-Acetoxymethylidene)benzonorbornadiene 3, prepared in one step by the addition of benzyne to 6-acetoxyfulvene 2, is hydrolysed in acid solution to form a 3:2-epimeric mixture of syn- and anti- 7-formylbenzonorbornadienes 4 and 5, respectively; the corresponding 7-hydroxymethylbenzonorbornadienes 6 and 9 were produced by reduction of the formyl isomers with sodium borohydride. Full article
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12 pages, 407 KiB  
Article
High-level Computational Study of the Site-, Facial- and Stereoselectivities for the Diels-Alder Reaction Between o-Benzoquinone and Norbornadiene
by Davor Margetic, Martin R. Johnston and Ronald N. Warrener
Molecules 2000, 5(12), 1417-1428; https://doi.org/10.3390/51201417 - 22 Dec 2000
Cited by 14 | Viewed by 10020
Abstract
Ab initio and DFT quantum chemical calculations have been applied to a study of the Diels-Alder reaction of o-benzoquinone as diene and norbornadiene as dienophile. Transition states for the different reactions are located and activation energies estimated. The prefered exo-π-facial selectivity [...] Read more.
Ab initio and DFT quantum chemical calculations have been applied to a study of the Diels-Alder reaction of o-benzoquinone as diene and norbornadiene as dienophile. Transition states for the different reactions are located and activation energies estimated. The prefered exo-π-facial selectivity and exo,endo-stereoselectivity exhibited in this cycloaddition are readily predicted using RHF/3-21G or higher levels of calculations. Differences between experimentally observed results and calculations may be explained by the postulation of a second, nonconcerted biradical mechanism leading to formation of hetero Diels-Alder products. Full article
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