摘要:

AbstractThe addition of reagents to trigonal carbon to give tetrahedral centers and its reverse involve the stereogenetic aspect known as face selection, which has ramifications throughout organic chemistry. Some of the root factors of face selection (e.g., steric and conformational) have long been understood in principle, but the electronic contribution of substituents and skeletal changes is controversial. The principal models for the electronic basis of face selection are those ofFelkin, AnhandCieplak. It is argued that none of the three are either right or wrong, but that the contribution each can make, varies from case to case. Each of them may become dominant depending on the reaction at issue.

ISSN:0165-0513    

DOI:10.1002/recl.19921110501

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractAziridine‐2‐carboxylic esters1were converted into bicyclic boroxazolidones3in a three‐step sequence. First, the ester groups were hydrolyzed either by sodium hydroxide or with lithium hydroxide in methanol. The salts thus obtained were acidified with acetic acid or through a weakly acidic ion‐exchange resin. Treatment of the zwitterionic aziridine‐2‐carboxylic acids2with triethyl‐borane in hexane gave boroxazolidones3in high yields. Boroxazolidone3g, obtained from optically active1gwas reconverted to the starting material by 8‐hydroxyquinoline without any loss of o

ISSN:0165-0513    

DOI:10.1002/recl.19921110502

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reactions of phenyl acetate(2), (trifluoromethoxy)benzene(3), (difluoromethoxy)‐benzene(4), 4‐(trifluoromethoxy)phenol(5), 4‐(trifluoromethoxy)phenyl methanesulfonate(6), 4‐(trifluoromethoxy)anisole(7)and 3‐(trifluoromethoxy)anisole(8)with SO3, in nitromethane have been studied. Upon reaction with SO3,2yields2‐4‐sulfonic acid (2‐4‐S); subsequently, transfer of the acetyl group takes place to yield the mixed anhydride of phenol‐4‐pyrosulfonic acid and acetic acid (9) or the corresponding hydrogen sulfate10, depending on the amount of SO3, used. Reaction of the α‐fluorinated anisoles3and4with SO3leads to sulfonation at the 4‐position only; however, on using both a high substrate concentration and an excess of SO3, some 2,4‐S2, is formed with4but not with3.On reaction of5with 0.8 mol‐equiv of SO3, in C2H3NO2, the hydrogen sulfate derivative (5‐O‐S) is formed; at 100°C, some isomerization to 5‐2‐S occurs. Upon reaction with 4.0 mol‐equiv of SO3, the initially formed hydrogen sulfate slowly yields the corresponding 2‐sulfophenyl hydrogen sulfate (5‐O,2‐S2). On using 6.0 mol‐equiv of SO3, the 5‐O,2‐S2is slowly converted into 6‐(trifluoro‐methoxy)benzo‐1,3,2,4‐dioxadithiin 2,2,4,4‐tetraoxide (11). Reaction of6with either 0.9 or 3.0 mol‐equiv of SO3, initially leads to insertion of sulfur trioxide in between the SO2CH3, and the adjacent O, yielding the 4‐(trifluoromethoxy)phenyl methanepyrosulfonate12. This species subsequently yields13and14. Reaction of7with SO3leads to sulfonation only at the 2‐position; eventually some sulfodemethylation to yield5‐2‐S takes place. Reacti

ISSN:0165-0513    

DOI:10.1002/recl.19921110503

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe synthesis of a dimyristoylglycerol peptide is reported. Starting from 1,2‐diisopropylidene‐sn‐glycerol, a 1,2‐dimyristoyl‐sn‐glycerol derivative has been synthesized which has been coupled to an immobilized peptide. After deprotection and cleavage from the resin, a diacylglycerol‐moiety‐containing lipopeptide was obtained which can be considered as a potential inhibitor of p

ISSN:0165-0513    

DOI:10.1002/recl.19921110504

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractHigh‐quality oligodeoxynucleotides having an 6‐O‐alkyl‐2′‐deoxyguanosine (alkyl = methyl, ethyl,n‐propyl orn‐hexyl) residue at a predetermined position can be obtained via a solid‐phase approach using the respective 2‐cyanoethylN,N‐diisopropylphosphoramidites of 5′‐O‐(4.4′‐dimethoxytrityl)‐protected 6‐O‐alkyl‐2′‐deoxyguanosines having a free exocyclic amino group, and 5′‐O‐(4‐4′‐dimethoxytrityl)N‐acyl‐protected (i.e., benzoyl and iso

ISSN:0165-0513    

DOI:10.1002/recl.19921110505

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19921110506

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19921110508

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19921110510

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19921110512

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY