摘要:

AbstractThe photochemical reactions of some (9‐demethylionyl)‐ and (9‐demethylionylidene)acetones and the corresponding acetophenones have been studied. The β‐isomers1aand1b, both under direct and triplet‐sensitized irradiation, undergo (E) ‐ (Z) isomerization of the 7,8‐double bond as the only observed reaction; with1a, the (E) ‐ (Z) isomerization is followed by a thermal 6e‐electrocyclization with formation of6. The α‐isomer2undergoes (E) ‐ (Z) isomerization both around the 7,8‐ and the 9,10‐double bond.The aliphatic β‐ionyl ketone3a, upon irradiation with λ 254 nm, undergoes a sigmatropic [1,5]‐hydrogen shift with formation of theretro‐isomer9, which, upon electronic excitation, undergoes aNorrish‐type‐II γ‐hydrogen abstraction with formation of the triene12. The related benzoyl ester4, upon λ 254 nm excitation, also exhibits the [1,5]‐hydrogen shift with formation of the photostableretro‐isomer17. Upon (n‐π*) excitation of the aromatic β‐ionyl ketone3bwith λ 350 nm, the triene12and acetophenone are formed as primary photoproducts. This photoconversion constitutes the first example of η‐hydrogen abstraction by a benzoyl chromophore directly leading

ISSN:0165-0513    

DOI:10.1002/recl.19851040402

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractIn this study, a series of acridinones and benzo‐fused acridinones have been used for the first time as efficient photosensitizers for the norbornadiene‐quadricyclane isomerization by near UV and visible iradiation. Their triplet energies (240‐280 kJ · Mol−1) are well below the value of 290 kJ · Mol−1which is generally assumed for norbornadiene. A mechanism is postulated involving an exciplex between sensitizer and norbornadiene.Limiting quantum yields of 0.5 and higher have been determined for this valence isomerization extrapolated to infinite norbornadiene concentration.Exciplex formation is supported by measurements of the rate of constantk2for quenching of excited sensitizer by norbornadiene, yielding values which are much smaller than the diffusion‐controlled quenc

ISSN:0165-0513    

DOI:10.1002/recl.19851040403

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractPenta‐O‐acetyl‐β‐D‐galactopyranose was converted in two steps into pentabromophenyl 1,2,3,4‐tetra‐O‐acetyl‐β‐D‐galactopyranoside. Short treatment of the latter with tetra‐n‐butylammonium hydroxide at 20°C, followed by acetylation, afforded crystalline 2,3,4‐tri‐O‐acetyl‐1,6‐anhydro‐β‐D‐galactopyranose. The same procedure could also be applied to the synthesis of the per‐O‐acetates of 1,6‐anhydro‐β‐cellobiose and 1,6‐anhydro‐β‐D‐glucopyranose. 2,3,4‐Tri‐O‐acetyl‐1,6‐anhydro‐β‐D‐glucopyranose could also be obtained in a one‐flask procedure by selective tosylation of D‐glucose at

ISSN:0165-0513    

DOI:10.1002/recl.19851040404

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractVarious 2‐[Ar(alk)ylsulfonyl]ethanols were prepared and subsequently converted into the corresponding phosphorodichloridites in almost quantitative yield via a convenient synthetic route. The versatility of the method, which obviates the necessity of a distillation step, is demonstrated by the preparation of other Ar(alk)yl phosphorodichloridites, including the unstable benzyl phosphorodichloridit

ISSN:0165-0513    

DOI:10.1002/recl.19851040405

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19851040406

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractThe results of themeta‐photocycloaddition of cyanoanisoles to cyclopentene are in agreement with a mechanism involving a dipolar species. The adducts undergo thermal and photochemical rearrangement

ISSN:0165-0513    

DOI:10.1002/recl.19851040407

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractSubstitution of the 2‐O‐triflyl function in 4‐O‐acetyl‐1,6‐anhydro‐3‐O‐anisoyl‐β‐D‐mannopyranose with the Cs‐salt of levulinic or benzoic acid affords 4‐O‐acetyl‐1, 6‐anhydro‐3‐O‐anisoyl‐2‐O‐levulinoyl(benzoyl)‐β‐D‐glucopyranoses. Coupling of 1,6‐anhydro‐2,3‐O‐(4‐methoxybenzylidene)‐β‐D‐mannopyranose with β‐D‐galactose pentaacetate in the presence of trimethylsilyl triflate affords a β(1→4) linked disaccharide the mannose unit of which can be co

ISSN:0165-0513    

DOI:10.1002/recl.19851040408

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19851040401

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY