A Novel Approach to the Synthesis of C-Glycosyl Compounds: The Wittig Rearrangement

Abstract

Partially protected benzyl α-and β-pyranosides undergo Wittig rearrangement reactions on treatment with strong bases in tetrahydrofuran to give hydroxymethylphenyl C-glycosyl derivatives. Two products were generally obtained and all Wittig rearrangement products retained the configuration at the migrating anomeric center. In benzene, benzyl 4,6-O-isopropylidene-β-D-glucopyranoside reacted with n-butyl lithium to give addition to the anomeric center accompanied by ring opening with loss of the aglycone. Allyl glycosides do not give Wittig rearrangement products.     

Novel 1,4-homofragmentation via an alpha-lactone

Conversion of an alpha,alpha-dichloroester to the corresponding alpha-keto acid was unexpectedly complicated by a novel 1,4-homofragmentation. Investigation of the kinetics of this reaction revealed a mechanism involving an alpha-lactone intermediate, which can lead to both the desired alpha-keto acid and the 1,4-homofragmentation, with the product distribution being dependent upon reaction conditions. This information allowed development of a process that affords the alpha-keto acid exclusively and should be generally applicable to the preparation of alpha-keto acids from alpha,alpha-dichloroesters or acids.     

Utilizing the Asymmetric Amino-Cope Rearrangement as a Novel Approach to Enantiomerically Enriched 3-Substituted Aldehydes

We report the asymmetric amino-Cope rearrangement of some novel 3-amino-1,5-diene substrates to yield enantiomerically enriched 3-alkyl and 3-aryl aldehyde products. We have developed a system that gives excellent and comparable levels of product enantiomeric excess (ee) for both alkyl- and aryl-substituted products. Our results have implications for the control of the mechanistic pathway of the amino-Cope rearrangement and thus its potential utility in asymmetric synthesis.     

A Concise Approach to the Synthesis of L-and D-Deoxyribose

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基于钯铜催化合成靛红类化合物的新方法

发展了一种合成靛红的新方法, 并进行了底物扩展, 得到了一系列靛红类化合物. 以N-烷基取代的丙烯酰苯胺类化合物为原料, 在醋酸钯、 碘化亚铜和氧气的催化及参与下, 以42%~87%的产率合成了N-烷基化的靛红衍生物. 利用该方法制备了23个靛红类化合物, 并提出了可能的反应机理. 该合成路线减少了保护基的使用, 简洁高效.     

Rearrangement of 3,5-dicyano-1,4-dihydropyridines to densely functionalized cyclopentadienes

3,5-Dicyano-1,4-dihydropyridines underwent ring contraction to give functionalized cyclopentadienes upon treatment with trifluoroacetic anhydride.     

A Concise Approach to the Synthesis of Carnosic Acid Type Diterpenes

AIDS has seriously affected human being's health and about 13.9 million people have been killed by AIDS in the world. So far, A. Paris et al1 found that Carnosic acid and its analogs posses inhibitory effect on HIV-1 protease and HIV virus replication activity. In order to clarify the structure-active relationship of this kind of compounds, a concise approach was designed, which is a convergent synthesis. Best to our knowledge, it is the first successful convergent route in total synthes…     

Asymmetric Induction via an Intramolecular Haloetherification Reaction of Chiral Ene Acetals: A Novel Approach to Optically Active 1,4- and 1,5-Diols

An asymmetric synthesis of chiral 1,4- and 1,5-diols has been developed from the ene acetals 1a and 1c, prepared from the corresponding aldehydes and chiral C(2)-symmetric diols, involving remote asymmetric induction as a key step. In the first step, treatment of 1 with I(coll)(2)ClO(4) in the presence of an alcohol afforded the macrocyclic acetals (3-5 and 7) in a highly stereoselective manner. Subsequent nucleophilic substitution of iodide followed by a Grignard reaction with complete retention of stereochemistry and a final deprotection of the diphenylethylene or diphenylpropylene unit successfully gave optically active 1,4- and 1,5-diols in good yields.     

Novel Photochemical Rearrangement of Styrylfurans

A conrotatory photocyclization , a novel [1,9] hydrogen shift, and a lateral ring opening are involved in the rearrangement of a series of 2-(4-alkylstyryl)furans 1 to 5-(3-alkylbutadienyl)benzo[b]furans 2 in dichloromethane. These novel photochemical rearrangements occur with good yields of isolated products.     

Novel access to 1,4-benzodiazepin-2-ones via the Buchwald reaction and application to the synthesis of novel heterocyclics

A new two step strategy for the preparation of 1,4-benzodiazepin-2-ones has been developed starting from the 2-halogenobenzophenone under Buchwald conditions (Pd(OAc)₂, XantPhos, Cs₂CO₃, dioxane 100 °C). This strategy has been extended to two 2-halogeno-3-benzoyl-azines (pyridines, pyridazines).     

Rearrangement of 2-amino-1-aryl-1,4-dihydropyridines

Heating of 2-amino-1-aryl-1,4-dihydropyridines in acidic aqueous media gives 2-arylamino-1,4-dihydropyridines. The reaction formally involves the migration of the aryl substituent from the endo-to exocyclic N atom. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1259–1260, July, 2006.     

Rearrangement of the intermediate 1,4-biradicals in photocycloaddition of cyclohex-2-enones to alkenes

Two unusual examples of enone/alkene photocycloaddition involving a rearrangement of the intermediate 1,4-biradical are presented. The first reaction proceedsvia the addition of one of the radical centers to a carbonyl C aton and subsequent bond cleavage,i.e., with rearrangement to a 1,3-biradical, while the second reaction involves abstraction of an H atom by one of the radical centers. The material was partly presented as an invited lecture by Paul Margaretha at the Sixth International Conference on the Chemistry of Carbenes and Related Intermediates (St. Petersburg, May 28–30, 1998). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 514–516, March, 1999.     

A Concise Semi-Synthetic Approach to Betulinic Acid from Betulin

Betulin was convert to betulinic acid using two different synthetic routes. The first approach involved an oxidation of betulin using Jones' reagent to betulonic acid and subsequent NaBH₄ reduction to betulinic acid. The second approach involved steps utilizing different protecting groups on the alcohol functional groups of betulin and Jones' oxidation to circumvent the isomerization of the secondary alcohol of betulinic acid.     

Novel ring transformation of quinolines to indole derivatives in two steps via 1,4-dihydroquinoline derivatives

Diphenyl 1-phenoxycarbonyl-1,4-dihydroquinoline-4-phosphonates 5c-g, obtained from the reaction of corresponding quinoline derivatives 1 with phenyl chloroformate and triphenyl phosphite in one step, were ozonized in CHCl₃ and CH₃COOH. Treatment of the resulting mixture with NaHCO₃ produced the 3-formyl-1-phenoxycarbonylindole derivatives 8a-e in high yields. The ring transformation of quinolines 1 to indoles 8 proceeds under mild conditions.     

Rearrangement of 2-butyne-1,4-diol to butyrolactone catalyzed by ruthenium complexes

The isomerization of 2-butyne-1,4-diol to butyrolactone catalysed by ruthenium complexes is described.     

Rearrangement of 1,4-benzodiazepin-2,4-diones to 3,l-benzoxazin-4-ones

Treatment of 7-chloro-3,4-dihydro-1H-1,4-benzodiazepin-2,5-dione (Ia) with refluxing acetic anhydride in the presence of pyridine afforded 6-chloro-2-methyl-4H-3,1-benzoxazin-4-one (IIa). A plausible reaction path for this novel rearrangement reaction is described: Ia → 4-acetyl-7-chloro-3,4-dihydro-lH-1,4-benzodiazepin-2,5-dione → 7-chloro-1,4-diacetyl-3,4-dihydro-lH-1,4-benzodiazepin-2,4-dione → IIa. When 7-chloro-3,4-dihydro-4-methyl-lH-1,4-benzodiazepin-2,5-dione (Ib), 3,4-dihydro-4-methyl-1H-1,4-benzodiazepin-2,5-dione (Id) and 3,4-dihydro-1-methyl-1H-1,4-benzodiazepin-2,5-dione (Ie) were allowed to react with acetic anhydride under conditions similar to those used for the rearrangement reaction, only acetylation occurred.     

Novel amine-containing biodegradable polyester via copolymerization of aspartic anhydride and 1,4-cyclohexanedimethanol

A novel biodegradable polyester having pendant amine functional groups was snythesized from N-(benzyloxycarbonyl)-L -aspartic anhydride ( 2 ) and 1,4-cyclohexanedimethanol ( 3 ) by polycondensation reaction using p-toluenesulfonic acid as a catalyst. The synthesized polymer 4 shows the characteristic ester carbonyl absorption peak at 1732 cm⁻¹ in the IR spectrum, and the NMR spectra were consistent with the IR data. Also, the elemental analysis showed that the experimental and calculated values were very close to each other. The weight-average molecular weight of the polymers ranged from 1140 to 5050 and increased with increasing reaction time. This new polymer would have the potential of a drug delivery biomaterial.