摘要:

AbstractOptically active oxirane‐2‐carboxylic esters, prepared from allylic alcohols employing the Sharpless epoxidation, were treated with sodium azide. The azido alcohols obtained were subsequently converted into aziridine‐2‐carboxylic esters by reaction with triphenylphosphine, in good yields and with high optical purity. Various racemic oxirane‐2‐carboxylic esters were subjected to the same sequence o

ISSN:0165-0513    

DOI:10.1002/recl.19921110101

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractRing‐opening reactions of 3‐arylaziridine‐2‐carboxylic esters with various nucleophiles are described. Racemic methyl 3‐(4‐methoxyphenyl)‐, 3‐phenyl‐ and 3‐(4‐nitrophenyl)aziridine‐2‐carboxylate (1a, 1band1c, respectively) were selected as substrates. In the absence of acid, no ring opening occurred. On treatment with ethereal hydrogen chloride,1agave a mixture of diastereomers2a, whereas1band1cgave mixtures of regioisomers2b/3band2c/3c, respectively. Boron‐trifluoride etherate catalyzed reaction of1awith benzenethiol and indole also resulted in the formation of diastereomeric ring‐opened products4aand6a, respectively, due to the electron‐releasing properties of the p‐methoxy group. Only C3 attack was observed. Under the same conditions,1band1cgave a cleanSN2‐type ring opening, leading to diastereomerically pure products4b, 4c, 6band6c. Reaction of1bwith acetic acid gave 7 in anSN2‐type ring opening at C3, followed by an O→N acyl shift. Treatment of enantiopure (+ )‐(2S,3R)‐1bwith benzenethiol, indole and acetic acid gave the corresponding enantiomerically pure β‐functionalized α‐amino acid derivatives. Functionalization of1bat nitrogen strongly increased the reactivity:N‐acylaziridine8isomerized totrans‐oxazoline11when tr

ISSN:0165-0513    

DOI:10.1002/recl.19921110102

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThermodynamic dissociation constants in various water‐organic solvent mixtures are given for benzylammonium, benzyldialkylammonium, and (2‐phenylethyl)ammonium ions. Deviations from the Hammett equation (Eqn. 1) are similar to those observed for carboxylic acids, but of opposite sign. The extended Hammett equation (Eqn. 3), containing the hydrophobic constant, π, yields good correlations. Derived secondary normal sigma values are exempli

ISSN:0165-0513    

DOI:10.1002/recl.19921110103

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

Abstract(All‐E)‐5‐demethyl‐8,16‐methanoretinal was prepared in both optical antipodes (1Rand 1S), as well as in their 9‐Zand13‐Zforms. The interaction of the 1Rand 1Sforms with bacterioopsin shows that there is a clear chiral recognition on the formation of the bacteriorhodopsin analogues, reflected in the rate of binding and ϵmaxvalues. The two bacteriorhodopsins with optically active chromophores have an identical λmaxvalue and show the same efficiency of the light‐driven proton pump. The absence of the 5‐methyl group leads to a 50% lower proton‐pump efficiency than the native system. In addition, for the racemic 5‐demethyl‐8,16‐methanoretinal, the 5‐2H, 7‐2H, 5,7‐2H2and 5,7,16a,16a‐2H4isotopomers in the various isomeric forms a

ISSN:0165-0513    

DOI:10.1002/recl.19921110104

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe UV spectra of the geometric isomers of the α‐bis(methoxyimino)alkanesI‐8and the structurally related conjugated (methoxyimino)isoxazolines11and13all exhibit a ππ* absorption band, of which the maxima with cyclohexane as solvent are between 216 and 268 nm, and 258 and 282 nm, respectively. The differences in λmaxare discussed in terms of variations in the degree of inter‐iminyl conjugation, as a result of (i) variations in the inter‐iminyl dihedral angle due to steric hindrance and (ii) variations in the ring strain and/or the dipolar repulsion of the two methoxyimino moieties, as with the three geometric isomers of the four‐membered ring compound1. The lower λmaxof (E,E)‐8 compared to (E,E)‐4 is ascribed to a lower degree of cross‐conjugation of the phenyl group with the planar α‐bis(methoxyimino) chromophore in the former compound; the absorption band of (E,E)‐8 is, in fact, similar to that of the aliphatic (E,E)‐5. The energy of the ππ* absorption maximum of the (E,E)‐α‐bis(methoxyimino)alkanes appears to be linearly related to that of the corresponding (E)‐α‐oxo oxime ethers with a slope close to unity, illustrating that the sensitivity for structural variations is very similar for the two types of compounds.X‐ray structure analysis showed the O‐N = C‐C = N‐O chromophore of (E,E)‐5, (E,E)‐8 and the (hydroxyimino)isoxazoline (E)‐10 in the crystalline

ISSN:0165-0513    

DOI:10.1002/recl.19921110105

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reactions of styrene derivatives1a‐14awith sulfur trioxide were studied in the temperature range −60 to 25°C using dichloromethane as solvent and 1.5 mol equiv. of dioxane as reactivity moderator. Reaction of styrene (1a) at low temperature yields the carbyl sulfate1cas the only observable intermediate in the ultimate formation of (E)‐2‐phenylethene‐1‐sulfonic acid (1d). The (phenyl) substituted styrenes3a‐5aclearly demonstrate the presence of the β‐sultones3b‐5bas the sole initial products leading to the corresponding carbyl sulfates3c‐5c. The initially formed β‐sultonebin the reaction of styrene derivatives3a‐5a, 9aand10awith 1.0 mol equiv. of SO3disproportionates to yield equal amounts of the corresponding carbyl sulfate and the starting styrene. This is thought to indicate that there is an equilibrium between the β‐sultone and the starting styrene. The group of the 1‐methyl‐substituted styrenes11a‐13aare an exception to the generally observed eventual conversion of the initial intermediates into the 2‐sulfonic acidsd, since they give the corresponding 3‐sulfonic acidsf.Mechanisms for the formati

ISSN:0165-0513    

DOI:10.1002/recl.19921110106

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractCondensation of R‐(+)‐1‐(2‐chlorophenyl)‐2,2‐dimethyl‐propan‐1,3‐diol (2) with a derivative (1) of 1‐formylcyclohexene substituted in the 3‐position with an acetoxy group proceeded with absolute stereospecificity at the acetal center. Catalytic alkylation of the π‐allyl complex obtained upon reaction with Pd with the anion of dimethylmalonate proceeded at the 3‐position of the cyclohexyl ring w

ISSN:0165-0513    

DOI:10.1002/recl.19921110107

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY