摘要:

AbstractThemetaphotocycloaddition of cyano‐ and (trifluoromethyl)‐substituted anisoles to cyclopentene has been investigated and the product ratios are shown to be compatible with a polar mechanism. The photochemical and thermal interconversions of the major adducts from 3‐cyanoanisole and cyclopentene have also been investi

ISSN:0165-0513    

DOI:10.1002/recl.19861050602

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractA systematic investigation of the alkaline degradation of monosaccharides is presented. The influence of several parameters upon the degradation reaction has been determined by analysis of the reaction products using HPLC and, in some cases, GC. The HO−and the monosaccharide concentrations markedly influence the final product composition with respect to both the amount of C1to C6acids and the formation of oligomeric acidic products, the so‐called>C6acids. Maximum yields of these>C6acids, up to 50 mol‐C6‐%, are obtained at an HO−concentration of between 10−3M and 10−2M when the monosaccharide concentration exceeds 10−2M. The presence of divalent calcium increases the retro‐aldolization of monosaccharides in alkaline medium, as illustrated by the enhanced production of lactic acid, by complexation with, for instance, d‐fructose. Borate partly protects monosaccharides against alkaline degradation through their borate esters, whilst the amount of saccharinic acids in the degradation product mixture is doubled. On the other hand, neither chloride and carbonate nor the reaction temperature influences the final product composition. Alkaline degradation experiments with pyruvaldehyde, glyceraldehyde and 1,3‐dihydroxyacetone, all assumed to be reaction intermediates, indicate that aldolization of (di)carbonyl compounds causes the formation of substanti

ISSN:0165-0513    

DOI:10.1002/recl.19861050603

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractOxidation of 2‐bromo‐6‐deuterio‐4,5‐dimethylphenol withFremy's salt, followed byin situreduction, yielded mainly 3‐bromo‐4,5‐dimethylpyrocatechol**, which affords evidence for a 1,3‐bromine shift during the oxidation. The same treatment of 2‐chloro‐4,5‐dimethylphenol yielded 4,5‐dimethylpyrocatechol with a minor amount of 3‐chloro‐4,5‐dimethylpyrocatechol. The 2‐iodo compound gave 4,5‐dimethylpyroc

ISSN:0165-0513    

DOI:10.1002/recl.19861050604

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe main product resulting from the reaction of d‐ribonolactone with benzaldehyde dimethyl acetal is a 2,3‐O‐benzylidene derivative of the 1,4‐lactone, and not the 2,4‐O‐benzylidene analogue of the 1,5‐lactone, as suggested previously. Chemical and physical evidence supports the re‐ass

ISSN:0165-0513    

DOI:10.1002/recl.19861050605

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe photochemistry (λ 300 nm) of the α‐oxo oxime ethers1aand2ahas been studied with the objective of detecting any γ‐H abstraction. Direct irradiation of (Z)‐1aresults only in (E)‐(Z) isomerization, whereas direct irradiation of the isomeric α‐oxo oxime ether1band the corresponding α‐diketone1cleads mainly to cyclobutanol formation. The absence of cyclobutanol formation with1ais ascribed to the higher angle of twist of the intercarbonyl‐iminyl angle of the reacting excited state of1a, as compared with those of both1band1c.The photodeuteration of the 7‐methyl hydrogens of2a, using C2H3O2H as (co)‐solvent, is a very inefficient process (Φ 7.0 × 10−5), and that of the benzylic hydrogens of the related ketone3ais even more inefficient (Φ ≤ 0.5 × 10−5). The inefficiency is ascribed mainly to the relatively low rate of γ‐H abstraction in the excited triplet (nπ*) state as well as to the very short life‐times of the ground state (Z)‐enols resulting from the relatively high rate of reketonization. The higher photodeuteration yield of the α‐oxo oxime ether2a, as compared with the benzylic hydrogens of3a, is ascribed to stabilization of the triplet 1,4‐diradical formed by γ‐hydrogen abstraction of the excited triplet (Z)‐2a, which results from electron

ISSN:0165-0513    

DOI:10.1002/recl.19861050606

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19861050607

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe synthesis of the first dinucleotide with a pentacoordinated phosphorus as the internucleoside linkage is described.31P‐NMR measurements revealed that the phosphorus pseudorotation proceeds with rapid stereomutatio

ISSN:0165-0513    

DOI:10.1002/recl.19861050608

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19861050601

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY