Radical deoxygenation of tertiary alcohols via trifluoroacetates

Trifluoroacetates of tertiary alcohols undergo deoxygenation by Ph₂SiH₂ in the presence of (^tBuO)₂ in excellent yields of the deoxy products without affecting the stereochemistry at β-carbon.     

Radical deoxygenation of tertiary alcohols

The thioformates of tertiary alcohols are smoothly reduced by tributyl tin hydride to the corresponding hydrocarbon in a radical chain reaction.     

原子转移自由基聚合法合成含羟基星状共聚物

以２－溴异丁酸季戊四醇四酯为引发剂在ＣｕＢｒ／ｂｐｙ催化下实施苯乙烯和丙烯酸β－羟丙酯原子转移自由基共聚合,结果表明聚合物的分子量与理论分子量接近,聚合反应具有活性聚合的特征。进一步对聚合产物进行ＧＰＣ,Ｈ－ＮＭＲ,ＩＲ和羟值滴定分析,表明合成的星状共聚合物中同时具有苯乙烯和丙烯酸β－羟丙酯结构单元,而且羟基在聚合物中近似均匀分布。     

Selective deoxygenation of aryl selenoxides by triaryl phosphites. Evidence for a concerted transformation

Triaryl phosphites selectively reduce aryl selenoxides to selenides. The Hammett plot of the reactions of para-phenyl substituted triaryl phosphites with diphenyl selenoxide gave ρ=+2.3, whereas with bis(p-methoxyphenyl) selenoxide, ρ=−2.1. The results are consistent with a concerted mechanism for the oxygen transfer from Se to P.     

Radical addition of dialkyl phosphites: Application in organic synthesis

Synthesis and application of phosphorylated esters, alcohols, ketones, epoxides, carbamates and carbamides, amino acids, and pyrimidines is reviewed.     

Regioselectivity among six secondary hydroxyl groups: selective acylation of the least reactive hydroxyl groups of inositol

We report the first, general and selective acylation of the least reactive hydroxyl group among six secondary hydroxyl groups of inositol in high yield, using very cheap and easy-to-make H(2)SO(4)-silica as the catalyst, providing easy access to bioactive molecules.     

Hybrid aminoglycoside antibiotics via Tsuji palladium-catalyzed allylic deoxygenation

Biosynthetically inspired manipulation of the antibiotic paromomycin led, in six high-yielding steps, to a ring A harboring an α,β-unsaturated 6'-aldehyde and an allylic 3'-methylcarbonate group. Tsuji deoxygenation in the presence of 5 mol % Pd(2)(dba)(3) and Bu(3)P granted access to a novel series of 3',4'-dideoxy-4',5'-dehydro ring A hybrids. The neomycin-sisomicin hybrid exhibited superior in vitro antibacterial activity to the parent compound neomycin.     

Rapid detection of hydroxyl groups on solid-phase

A rapid method for the qualitative detection of hydroxyl groups on solid-phase has been developed. The method employs N-methylisatoic anhydride to derivatise resin-bound substrates possessing free hydroxyl functionality. The resultant fluorescent ester can be detected by visualisation under a standard laboratory UV lamp at 365 nm excitation.     

Development of trityl-based photolabile hydroxyl protecting groups

A series of trityl-based photolabile hydroxyl protecting groups have been examined. These PPGs evolve from the traditional acid-labile trityl protecting group with proper electron-donating substituents. Structure-reactivity relationships have been explored. A m-dimethylamino group is crucial to achieve high photochemical deprotection efficiency. The o-hydroxyl group in 8 greatly improves the yield of the photochemical deprotection reaction, compared with the corresponding o-methoxyl-substituted counterpart 7. However, comparison between the photoreactions of 9 and 11 does not show similar structural relevance. The PPG in ether 1 (i.e., DMATr group) is structurally simple and easy to prepare and install. Its deprotection can be successfully carried out with irradiation of sunlight without requirement of photochemical devices.     

Direct selective and controlled protection of multiple hydroxyl groups in polyols via iterative regeneration of stannylene acetals

A direct selective protection (O-benzylation) of two or more hydroxyl groups in polyols displaying diverse structural patterns was made possible by the establishment of conditions that enable an efficient turnover for the Bu₂Sn group, initially at the corresponding stannylene acetals (only ∼1.0 mol equiv of Bu₂SnO was employed). It was also demonstrated that one might exert control over the number of protected groups, by means of appropriate tuning of reaction conditions. The feasibility of a substoichiometric (tin source) catalytic protocol was demonstrated as well.     

Microdetermination of hydroxyl groups in polymers using phosgene

Summary The phosgene method for the determination of terminal hydroxyl groups in polymers has been applied on the microscale. Its lower practical limit is 0.01 mmol of alcoholic hydroxyl. The reaction time, and the amount of solvent and phosgene have been reduced. The hydrolysis of the chloroformate formed by reaction with phosgene has been simplified: Reaction withm-chloroaniline yieldsm-chloroaniline hydrochloride, which is titrated with standard silver nitrate using a chloride-ion selective electrode.The method has been applied to the determination of the hydroxyl content of polyesters and poly(ethylene oxides). It seems particularly promising for the determination of hydroxyl in alpha-epoxides.

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Zusammenfassung Die Phosgenmethode zur Bestimmung terminaler Hydroxylgruppen in Polymeren wurde in den Mikromaßstab übertragen. Die untere Grenze ihrer Anwendbarkeit beträgt 0,01 Millimol alkoholisches OH. Die Reaktionszeit, die Lösungsmittelmenge und Phosgenmenge wurden herabgesetzt. Die Hydrolyse des bei der Reaktion mit Phosgen entstehenden Chloroformats wurde vereinfacht: die Umsetzung mitm-Chloranilin ergibtm-Chloranilinchlorhydrat, das mit einer Standard-Silberlosung unter Verwendung einer chloridspezifischen Elektrode titriert wird.Das Verfahren wurde zur Bestimmung des Hydroxylgehaltes von Polyestern und Polyäthylenoxiden verwendet. Für die Hydroxylbestimmung in-Epoxiden scheint es besonders geeignet zu sein.

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This work was performed under the auspices of the U.S. Atomic Energy Commission.

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Parts of this paper were presented at the Second JANNAF Propellant Characterization Working Group Meeting at Las Vegas, Nevada, November 1, 1971.     

Epoxides as alkene protecting groups. A mild and efficient deoxygenation

Dimethyl diazomalonate smoothly deoxygenates epoxides to alkenes with rhodium(II) acetate catalysis.     

Study of the mechanism of the thermochemical reaction of polyimides with hydroxyl groups via vibrational-spectroscopy and quantum-chemistry methods

The thermochemical transformation of polyimides with one hydroxyl group in a diamine fragment that leads to changes in the polymer structure is studied. It is found that in an inert atmosphere in the temperature range 400–450°C, an intramolecular thermochemical reaction accompanied by evolution of carbon dioxide occurs. The FTIR spectra of all studied polyimide films prepared from different solvents and annealed in an inert atmosphere in the range 25–450°C show similar changes that do not agree with the structures of the reaction products (polybenzoxazole and polydehydrocyclobutabenzene) described in the literature. Possible reaction paths are calculated via quantum-chemistry methods. A mechanism of the intramolecular thermochemical transformation and the related structure of the formed polymer (aromatic lactam) are proposed.     

Conformational preferences for hydroxyl groups in substituted tetrahydropyrans

Quantum mechanical (ab initio and semiempirical) and force field calculations are reported for representative torsion potentials in several tetrahydropyran derivatives. The overall agreement between the various methods is quite good except that the AMBER torsion profiles are sensitive to the choice of atomic point charges. Using electrostatic potential (ESP) derived atomic point charges determined with the STO-3G basis set we find that AMBER is able to match the best quantum mechanical results quite well. However, when the point charges are derived using the 6-31G* basis set we find that scaling the intramolecular electrostatic nonbond interactions is necessary. AM1 does not work very well for these compounds when compared to the ab initio methods and, therefore, should only be used in cases when ab initio calculations would be prohibitive. Based upon our results we feel that any force field that makes use of 6-31G* ESP derived atomic point charges will need to scale intramolecular interactions. Implications of scaling intramolecular interactions to the development of force fields based on 6-31G* ESP derived atomic point charges are discussed. © 1992 by John Wiley & Sons, Inc.