摘要:

AbstractThe photochemical reaction ofortho‐quinones with triarylketenimines4yields quantitatively the dihydrodioxin derivatives5via a (4+ 2)‐cycloaddition. Kinetic studies on the photochemical reaction of phenanthrenequinone (PQ) withN‐(p‐tolyl)dipheriylketenimine show that the reaction proceeds irreversibly, probably via an exciplex of triplet PQ with the CC double bond and an allylic biradical:k2= (1.18 ± 0.03)·1091·mol−1·s−1at 25°C in benzene (Scheme 2). Competition experiments between triplet PQ andN‐phenyl‐substituted triphenylketenimines (Ph2C = C = N − C6H4− X) gave a good correlation between the relative rate constants and the normalHammettσ‐constants ρ = −0.31, which indicates the absence of conjugation between the substituent X and the reaction centre at the C  C double bond and confirms the electrophilic character of triplet phenantrenequinone. From theTaft's DSP equation it follows that the

ISSN:0165-0513    

DOI:10.1002/recl.19851040202

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractQuenching of the bicyclo[5.4.1]dodecapentaenyl cation1with LiOMe/MeOH affordedendo‐4‐methoxy‐syn‐bicyclo[5.4.1]dodeca‐2,5,7,9,11‐pentaene with the methoxy group in a highly crowded position. The remarkable reactivity of cation1can be explained by the intermediacy of asyntransition state having a homocyclopropenyl‐type cation at theexoface of the carbon skeleton. Quenching of1with the more bulky acetate anion gave the thermodynamically favouredexo‐4‐a

ISSN:0165-0513    

DOI:10.1002/recl.19851040203

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractA new method is described for the synthesis of symmetrical and unsymmetrical diketones. Particularly good results are obtained in the synthesis of 1,6‐ and 1,5‐diketones. Procedures are reported for 1,2‐diketones. The moderate results obtained for 1,4‐diketones and the lack of success for 1,3‐diketones are

ISSN:0165-0513    

DOI:10.1002/recl.19851040204

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractThe cesium salts ofN‐[(9‐fluorenylmethoxy)carbonyl]‐L‐serine (Fmoc‐Ser,1a)*** and ‐L‐threonine (Fmoc‐Thr,1b) were treated with 2‐(bromomethyl)‐9,10‐anthraquinone (Maq‐Br), yielding Fmoc‐Ser‐OMaq (2a, 79%) and Fmoc‐Thr‐OMaq (2b, 74%). HgBr2‐catalyzed glycosylation with 2,3,4,6‐tetra‐O‐acetyl‐α‐D‐galactopyranosyl bromide gave Fmoc‐Ser(Ac4βGal)‐OMaq (3a, 89%) and Fmoc‐Thr(Ac4βGal)‐OMaq13b, 53%). Fmoc‐Ser(Ac4βGal)‐OH (4), obtained by reaction of1awith Na2S2O4(88%), was condensed with H‐Ala‐OMaq using the DCC/HOBt method (83%). The Fmoc‐Ser(Ac4βGal)‐Ala‐OMaq(5), thus obtained, wasNα‐deprotected with morpholine and coupled with Fmoc‐Ala using water soluble carbodiimide in the presence of HOBt to yield Fmoc‐Ala‐Ser(Ac4βGal)‐Ala‐OMaq (6, 59%). The fully deprotected glycotripeptide (8) was obtained from6by successive treatment with Na2S2O4, morpholine and hydrazine hydrate (81%).The comp

ISSN:0165-0513    

DOI:10.1002/recl.19851040205

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractCationic cyclization of 2‐[7‐(3‐methoxyphenyl)‐(E)‐4‐heptenyl]‐3‐methyl‐2‐cyclopentenol (1c) produced 3‐methoxy‐17‐methyl‐C‐homo‐1,3,5(10),13(17)‐gonatetraene (3c) and its 1‐methoxy isomer2c. Epoxidation of3cwithtert‐butyl hydroperoxide in the presence of molybdenum hexacarbonyl produced the corresponding 13α, 17α‐epoxide14as the major product, which, in three steps, was converted into C

ISSN:0165-0513    

DOI:10.1002/recl.19851040206

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

摘要:

AbstractFour isomeric 3,4‐dihydro‐2,2′‐pyrromethen‐5(1H)‐one E/Z pairs were prepared which show not only a photochemical E/Z isomerization but also a photo‐Fries type

ISSN:0165-0513    

DOI:10.1002/recl.19851040207

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19851040201

出版商:WILEY‐VCH Verlag    

年代:1985

数据来源: WILEY