Synthesis of 1,6-Dideoxynojirimycin, 1,6-Dideoxy-D-allo-nojirimycin,and 1,6-Dideoxy-D-gulo-nojirimycin via Asymmetric Hetero-Diels-Alder Reactions

Asymmetric Diels-Alder reaction of sorbaldehyde O-methyloxime 1d with chiral chloronitroso derivative 2 of D -mannose, followed by osmylation of the primary cycloadduct, led to diol 6a with excellent enantioselectivity (ee > 99%; Scheme 1). Catalytic hydrogenolysis of 6a gave 1,6-dideoxy-D -allo-nojirimycin ( 7a ). Nucleophilic ring opening of cyclic sulfate 8 allowed a straightforward synthesis of 1,6-dideoxynojirimycin ( 11 ) and of 1,6-dideoxy-D -gulo-nojirimycin ( 12 ; Scheme 2).     

Ring Closure Reactions of Chalcones Using Microwave Technology

The synthesis of heterocyclic compounds containing pyrimidine, pyrazoline, isoxazoline and cyclohexenone ring from chalcone derivatives containing anisole and 3′4′-methylenedioxy phenyl ring under ‘dry conditions’ using microwaves and by conventional methods are described.     

Mean amplitudes of vibration and perpendicular amplitude correction coefficients for 1,2,4,5-hexatetraene and 1,2,4-pentatriene

Mean amplitudes of vibration (u) and perpendicular amplitude correction coefficients (K) for 1,2,4,5-hexatetraene and 1,2,4-pentatriene were computed from spectroscopic data. Values at 298°K for all interatomic distances are given and discussed.     

Synthesis of C-Disaccharides An Unusual Ring Closure Reaction

Abstract

Reaction of the 4-C-lithiomethyl intermediates, obtained from 4-deoxy-4-C-iodomethylglucopyranosides 5a,b, with open-chain glucose derivative 8 afforded 4-deoxy-4-C-heptitylglucopyranosides 9a,b. Mesylation of the newly generated hydroxy group and then desilylation gave 11a,b which were subjected to ring closure under basic conditions. Surprisingly, no C-bridged cellobiosides 12a,b (or, alternatively the corresponding maltosides) were obtained as major products; with loss of one benzyl alcohol residue the furanosides 13a,b were preferentially formed. Their generation and structural assignment is discussed.     

Synthesis of Benzodiazepines Through Ring Opening/Ring Closure of Benzimidazole Salts

Pyrido-benzodiazepine derivatives are undoubtedly one of the most important structural motifs in the marketed drugs and the drug candidates. Commonly synthetic methods for construction of the benzodiazepine ring derivatives are based on the condensation reactions of two highly functionalized synthons. The development of synthesis for these compounds, however, is hampered by the regioselectivity and atom economy. In this work, a one-step synthesis of pyrido-benzodiazepine backbones and its analogues is achieved through continuous ring-opening hydrolysis of benzimidazole salts and intramolecular C−H bond activation. The reaction mechanism is explored by control experiments and density functional theory (DFT) calculations.     

3-芳基-6-甲基-1,6-二氢-1,2,4,5-四嗪及其衍生物的合成和晶体结构

以乙腈和芳基腈为原料, 经过醚化、环化和还原三步方便且有效地合成了3-芳基-6-甲基-1,6-二氢-1,2,4,5-四嗪, 并在此基础上合成了一系列新的3-芳基-6-甲基-1,6-二氢-1,2,4,5-四嗪衍生物, 通过元素分析, ¹H NMR, IR和HRMS对这些化合物进行了表征. 对化合物N-邻甲基苯-3-苯基-6-甲基-1,6-二氢-1,2,4,5-四嗪-1-甲酰胺(5a)的X射线晶体衍射研究表明: 其属于单斜晶系, P2_{1 /c空间群, 晶胞参数a＝1.3941(6) nm, b＝0.5675(2) nm, c＝2.0614(8) nm; α＝γ＝90°, β＝102.055(6)°; V＝1.5949(11) nm³, 此类化合物的四嗪环采用不对称船式结构, 且具有同芳香性.}     

Ab Initio calculations on the isomerization of the dimethylene cyclobutene and 1,2,4,5-hexatetraene radical cations to the benzene structure

Ab initio calculations at the MRCI//ROHF/6-31G** level suggest that stable C₆H₆ radical cations formed from dimethylene cyclobutene and 1,2,4,5-hexatetraene either retain the structure of the parent neutral molecule or isomerize to the benzene structure. The previous suggestion from photodissociation experiments that part of the ions from dimethylene cyclobutene isomerize to the 1,2,4,5-hexatetraene structure is not supported by the present results.     

Formation of Thermally Robust Frustrated Lewis Pairs by Electrocyclic Ring Closure Reactions

The phosphorus/boron‐substituted hexatriene systems 6 undergo thermally induced electrocyclic ring closure to yield the cyclohexadiene‐derived P/B frustrated Lewis pairs (FLPs) 7 . Subsequent TEMPO oxidation gives the phenylene‐bridged FLPs 8 . Both systems activate dihydrogen and the thermally robust FLPs undergo carbon–carbon coupling reactions at a mesityl group upon treatment with dimethyl acetylenedicarboxylate at elevated temperatures.     

抗癌大环化合物的环合方法

大环化合物具有广泛的生物活性.一些具有抗癌活性的天然大环化合物已开发成上市药物或应用于临床研究.在抗癌大环化合物的合成中,环合步骤是整个合成过程中的关键,同时也是难点所在.目前已经发展出了一些方便实用的环合方法.文章以具有抗癌作用的大环化合物为例,简要介绍各种常用的大环环合方法及应用.