摘要:

AbstractThe photocyclization of 2‐styrylbenzo[c]phenanthrene (1) inn‐butylamine yields a mixture of hexahelicene (3) and two dihydrohexahelicenes (5and6). Both dihydrohexahelicenes could be isolated from the irradiation mixture as pure compounds by chromatography on a silica gel coated withR( ‐ )‐TAPA, a chiral stationary phase developed for the resolution of the enantiomers of hexahelicene (3). The NMR spectra of 5,6‐dihydrohexahelicene (5) and 7,8‐dihydrohexahelicene (6) exhibit remarkable differences in the aromatic region. These differences are attributed to the location of the alicyclic ring in the hexahelicene skeleton. The X‐ray structure analyses of the dihydrohexahelicenes5and6demonstrate that, in the crystalline state, both isomers occur in only one of two possible conformations. The NMR spectra of the two compounds lead to the conclusion that, in solution, the same conformation as in the solid state is highly preferred, although the existence of the second conformation cannot be completely excluded. Structural analyses by forcefield calculations corroborate th

ISSN:0165-0513    

DOI:10.1002/recl.19881071002

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe homogeneous reactions of 1,4‐dihydroxybenzene (1), its monomethyl (2) and dimethyl ether (3) and 2‐3‐sulfonic acid in 68‐105% H2SO4at 25°C have been studied and isomer distributions and rate coefficients for the various subsequent sulfonations, as well as the equilibrium data for the sulfation (‐OH⇌ ‐OSO3H), are reported. For2, the ratio of 2‐ to 3‐sulfonation decreases upon increasing the sulfuric acid concentration from 68‐98.5% H2SO4, due to a gradual change‐over in the effective sulfonating entity from H3SO4+to H2S2O7. For1‐2‐sulfonic acid (1‐2‐S),2‐2‐S and2‐3‐S, the ratios of 5‐ to 6‐sulfonation are allca.25:75, whereas3‐2‐S only yields the 5‐sulfonic acid. Demethylation of the sulfonic acids of2and3in ≤98.5% H2SO4is of minor importance, but plays a major role in 105.0% H2SO4, the eventual products being the bis(hydrogen sulfate)s10and15, the tricyclic bis(sulfate sulfonate anhydride)11and the bicyclic hydrogen sulfate16.Mechanisms for the sulfodemethylation and for the cyclization of the 2‐sulfophenyl hydrogen sulfate moiety to the 1,3,2,4‐be

ISSN:0165-0513    

DOI:10.1002/recl.19881071003

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractSilylation of a H‐phosphonate diester withN, O‐bis(trimethylsilyl)acetamide ortert‐butyldimethylsilyl chloride affords 3′,5′‐internucleotidic phosphite triester intermediates. Arbusow reaction of the latter compounds with appropriate halogenides gives the corresponding phosphonate

ISSN:0165-0513    

DOI:10.1002/recl.19881071004

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractReactions of11C recoil atoms with C6H6in the presence of O2lead to the formation of high yields of labelled C6H5CHO in the gaseous (6%) and liquid (8‐10%) phase, whereas none was detected in the solid phase. For the liquid phase, 63% of the11C activity in C6H5CHO is in the ‐CHO group, while 37% is part of the aromatic ring; in the case of gaseous C6H6with 37% O2, the amount of11C in the ring is only 11%. The reactions possibly leading to the formation of [11C]C6H5CHO and the11C distribution over the molecule are discus

ISSN:0165-0513    

DOI:10.1002/recl.19881071005

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe syntheses of two (spacer‐containing and choline‐phosphate‐deficient) analogues (12eand12h, Scheme 2) of a fragment of the C substance fromS. pneumoniaetype 1 are presented. Starting from 1,6:2,3‐dianhydro‐ß‐D‐talopyranose (la), the “building block” 1‐O‐(3,6‐di‐O‐acetyl)‐2‐azido‐4‐O‐benzyl‐2‐deoxy‐ß‐D‐galactopyranosyl)‐2,3,4‐tri‐O‐benzyl‐D‐ribitol (6b) was obtained in six steps (Scheme 1). A second “building block” (9e), containing a protected propanolamine spacer, was prepared in five steps, starting from 2,3,4,6‐tetra‐O‐acetyl‐α‐D‐glucopyranosyl bromide (7). The building blocks6band9ewere coupled (Scheme 2) usingbis(1‐benzotriazolyl) 2‐chlorophenyl phosphate (10) to give the fully protected phosphotriester derivative12a. Complete deprotection of compound12avia two different routes afforded β‐D‐GalNH2p‐(1 ŕ l)‐ribitol‐5‐phosphate‐6‐β‐D–Glcp

ISSN:0165-0513    

DOI:10.1002/recl.19881071006

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effects of ultrasound on conventional Freudenberg‐type benzylidenation reactions of some alkyl D‐glycopyranosides is described. A considerable enhancement in the rates of formation of the expected acetals was observed. The pure products were obtained in good yields. Some of the crude air‐dried products were suitable for direct derivatis

ISSN:0165-0513    

DOI:10.1002/recl.19881071007

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractCoupling of properly protected repeating tetrasaccharide units ofHaemophilus (Actinobacillus) pleuropneumoniaecould be realized by regioselective phosphorylation.

ISSN:0165-0513    

DOI:10.1002/recl.19881071008

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881071010

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881071011

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881071001

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY