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1978 (1)
1Author    Claudia Bäk, Klaus PraefckeRequires cookie*
 Title    Photoreaktionen 2.2'-dihalogensubstituierter Benzoinether und Benzildimethylmonoketale in Lösung 1 Photoreactions of 2,2'-Dihalogen Substituted Benzoin Ether and Benzildimethylmonoketals in Solution  
 Abstract    The synthesis of a,a'-dihalogenated benzoin ether 6 and benzildimethylmonoketals 7 are discribed. Their reaction behavior under UV irradiation and electron impact conditions are discussed in comparison with those of arylesters 1 of seleno and thiobenzoic acid. The photoproducts of 6 and 7 are separated and identified with help of column or vaporphase chromatography. Photoinduced a-cleavages of 6 and 7 produce 2-halogenbenzoyl radicals 9 and a-monomethoxybenzyl radicals 10 or a,a-dimethoxybenzyl radicals 15 resp., which undergo four different stabilization reactions under formation of 1) 2-halogenbenzaldehydes 12 from 9 by hydrogenabstraction, 2) 2,2'-dihalogenbenzils 11 and l,2-di(2-chlorophenyl)-1,2-dimethoxyethan (13) via dimerization of 9 or 10 resp., 3) methylesters 16 of 2-halogen-benzoic acids by /^-elimination of methylradicals from 15, and 4) 2-halogenacetophenones 17 via combination of 9 with methylradicals from 15. In addition to these photoproducts 2-phenylbenzoic acidester 18, benzaldehyde (19), and acetophenone (20) are formed by photosubstitution of halogens in benzaldehydes 12 as well as in acetophenones 17 against hydrogen and in benzoic acid-esters 16 against phenyl resp. Independent photoexperi-ments prove 1) the formation of 2-phenylbenzoic acidester 18 by halogen-phenylreplace-ment in 16 and 2) that chlorine is easier than bromine, both in orZ/io-position to a carboxyl function, substituted by phenyl. No photoproducts {e.g. 8 or 14) are formed by substitution of halogen in the 2-halogenbenzoyl part of a-cleavage against neither a-monomethoxybenzyl nor a,a-dimethoxybenzylradicals resp. as expected like the photoinduced formation of selenoxanthones or thioxanthones 2 from selenol-or thiolesters 1. 
  Reference    (Z. Naturforsch. 33b, 106—112 [1978]; eingegangen am 5. Oktober 1977) 
  Published    1978 
  Keywords    Carbonyl Compounds, a-Cleavages, Free Radicals, Aromatic Photosubstitutions 
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 TEI-XML for    default:Reihe_B/33/ZNB-1978-33b-0106.pdf 
 Identifier    ZNB-1978-33b-0106 
 Volume    33 
2Author    Reinhard Lüdersdorf, Jürgen Mai, Klaus PraefckeRequires cookie*
 Title    Synthese S-substituierter Benzile und einiger gehinderter Biphenyle [1] Synthesis of S-Substituted Benzils and Some Hindered Biphenyls [1]  
 Abstract    Three methylthio and/or methylsulfinyl substituted benzils (2, 6 and 7) have been synthesized on photo-or thermochemical routes, respectively. Photodecarboxylation of some new different substituted mesityl benzoates (1 a-e) leads to hindered biphenyls (3 a-e) accompanied sometimes by aldehyde (4a-c) and benzil formation (2) due to compatitive a-cleavage and subsequent stabilization processes of such generated free aroyl radicals. A short summary on constitutional conditions for intramolecular photoredox reactions of ortho functionalized aryl sulfinyl compounds is presented. 
  Reference    Z. Naturforsch. 35b, 1420—1425 (1980); eingegangen am 28. April 1980 
  Published    1980 
  Keywords    Photodecarboxylations, a-Cleavages, Photoredox Reactions, Sulfoxides 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-1420.pdf 
 Identifier    ZNB-1980-35b-1420 
 Volume    35 
3Author    Klaus Beelitz», Klaus Praefcke, -A, Salo GronowitzRequires cookie*
 Title    Pyrido [2,3-d] thieno [3,2-b] [6H]thiopyran - ein neues heterocyclisches Ringsystem [1] Pyrido [2,3-d]thieno[3,2-b] [6 H]thiopyran - a New Heterocyclic Ring System [1]  
 Abstract    UV irradiation of S-(3'-thienyl)2-chloro-thionicotinate (1) in benzene solution leads via dehydrohalogenation and cj clization in competition to a-cleavage to formation of thio-lactone 2 besides aldehyde 3 and disulphide 4. 2 contains a new heterocyclic ring system which has been confirmed by spectroscopic methods. Einführung 
  Reference    Z. Naturforsch. 34b, 1573—1575 (1979); eingegangen am 4. Juli 1979 
  Published    1979 
  Keywords    Organic Sulfur Compounds, Heterocycles, Thiolester, a-Cleavage, Dehydrohalogenation, Photocyclization, Aromatic Photosubstitution 
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 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-1573.pdf 
 Identifier    ZNB-1979-34b-1573 
 Volume    34