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Photocycloaddition Reactions (photocycloaddition + reaction)
Selected AbstractsPhotocycloaddition Reactions of 2-(Alk-3-en-1-ynyl)cyclohex-2-enonesHELVETICA CHIMICA ACTA, Issue 12 2008Janne Möbius Abstract The newly synthesized 2-(alk-3-en-1-ynyl)cyclohex-2-enones 4 undergo photodimerization (chemo- and regio-)selectively at the exocyclic CC bond to give diastereoisomeric mixtures of 1,2-dialkynyl-1,2-dimethylcyclobutanes. On irradiation of 4 in the presence of 2-chloroacrylonitrile, cyclobutane formation occurs again (chemo- and regio-)selectively at the exocyclic CC bond to afford diastereoisomeric mixtures of 2-alkynyl-1-chloro-2-methylcyclobutanecarbonitriles. Similarly, compounds 4 undergo photoaddition to 2,3-dimethylbuta-1,3-diene exclusively at the exocyclic CC bond to afford mixtures of [2+2] and [4+2] cycloadducts. [source] Photocycloaddition Reactions of 5,5-Dimethyl-3-(3-methylbut-3-en-1-ynyl)cyclohex-2-en-1-oneHELVETICA CHIMICA ACTA, Issue 3 2008Inga Inhülsen Abstract The title cyclohexenone 1d undergoes photodimerization selectively at the exocyclic CC bond to give a 1,:,1 mixture of 1,2-dialkynyl-1,2-dimethylcyclobutanes 6 and 7. On irradiation in the presence of 2,3-dimethylbuta-1,3-diene, 1d affords bicyclo[8.4.0]tetradeca-1,2,3,7-tetraen-11-one 9. This , formal , (6+4)-cycloadduct undergoes quantitative isomerization to 3-cycloheptadienyl-2,5,5-trimethylcyclohex-2-enone 11 on treatment with basic silica gel. [source] Regioselective [2 + 2]-Photocycloaddition Reactions of Chiral Tetronates , Influence of Temperature, Pressure, and Reaction Medium.CHEMINFORM, Issue 28 2007Martin Fleck Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Diastereo- and Enantioselective Intramolecular [2+2],Photocycloaddition Reactions of 3-(,,-Alkenyl)- and 3-(,,-Alkenyloxy)-Substituted 5,6-Dihydro-1H -pyridin-2-onesCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2010Dominik Albrecht Dr. Abstract 3-(,,-Alkenyl)-substituted 5,6-dihydro-1H -pyridin-2-ones 2,4 were prepared as photocycloaddition precursors either by cross-coupling from 3-iodo-5,6-dihydro-1H -pyridin-2-one (8) or,more favorably,from the corresponding ,-(,,-alkenyl)-substituted ,-valerolactams 9,11 by a selenylation/elimination sequence (56,62,% overall yield). 3-(,,-Alkenyloxy)-substituted 5,6-dihydro-1H -pyridin-2-ones 5 and 6 were accessible in 43 and 37,% overall yield from 3-diazopiperidin-2-one (15) by an ,,,-chloroselenylation reaction at the 3-position followed by nucleophilic displacement of a chloride ion with an ,-alkenolate and oxidative elimination of selenoxide. Upon irradiation at ,=254,nm, the precursor compounds underwent a clean intramolecular [2+2] photocycloaddition reaction. Substrates 2 and 5, tethered by a two-atom chain, exclusively delivered the respective crossed products 19 and 20, and substrates 3, 5, and 6, tethered by longer chains, gave the straight products 21,23. The completely regio- and diastereoselective photocycloaddition reactions proceeded in 63,83,% yield. Irradiation in the presence of the chiral templates (,)- 1 and (+)- 31 at ,75,°C in toluene rendered the reactions enantioselective with selectivities varying between 40 and 85,%,ee. Truncated template rac - 31 was prepared as a noranalogue of the well-established template 1 in eight steps and 56,% yield from the Kemp triacid (24). Subsequent resolution delivered the enantiomerically pure templates (,)- 31 and (+)- 31. The outcome of the reactions is compared to the results achieved with 4-substituted 5,6-dihydro-1H -pyridin-2-ones and quinolones. [source] | ||||||||||