Reactions of perfluorodimethylketene with alcohols,amines, and acids

Conclusions Perfluorodimethylketene is a good acylating agent for alcohols and amines and both mineral and organic acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, no. 7, pp. 1265–1267, July, 1966.     

Oxidation of alcohols by “activated” dimethyl sulfoxide. a preparative,steric and mechanistic study

The oxidation of primary, secondary, allylic, benzylic, hindered and bicyclic alcohols with dimethyl sulfoxide (DMSO) “activated” by numerous electrophiles was studied: yields of carbonyls, by-products and recovered alcohols were quantitatively determined. Pathways for carbonyl and by-product formation are presented. Generally, yields of carbonyls increase with increased steric hindrance in the alcohols. Steric effects of tertiary amines, used for basification, were also investigated, and the results are consistent with the suggested reaction pathways. Among previously unreported “activators,” oxalyl chloride is the most generally effective; yields of carbonyls are typically over 95%. Thionyl chloride is also a satisfactory “activator” although yields of carbonyls are not quite as high. An improved method of preparation of alkyl methylthiomethyl ethers, by-products of the oxidation process, is reported.     

Reactions of acetylenes with transition metals : VII steric effects in the oligomerization of diarylacetylenes

The synthesis of ortho-substituted diphenylacetylenes and their behaviour toward dichlorobis(benzonitrile)palladium(II) are described. The influence of steric factors on the oligomerization is discussed.     

Reactions of hexafluorobenzene and pentafluorophenylamino compounds with amides and anilides (steric effects)

Contrary to N-lithium-N-methylanilide and N-lithium-diphenylamide, trimethyl-N-lithium-N-phenyl-silylamide gave with hexafluorobenzene in molar ratio 2:1, only the monosubstituted compound. Competitive reactions gave the following order of reactivity toward N-lithiumanilide: 2,3,4,5,6-pentafluorotriphenylamine > 2,3,4,5,6-pentafluoro-N-methyl-diphenylamine > hexafluorobenzene ? trimethyl-2,3,4,5,6-pentafluoro-N,N-diphenyl-silylamine. A reason for the low reactivity of trimethyl-2,3,4,5,6-pentafluoro-N,N-diphenyl-silylamine against aromatic amides has been proposed.Some new aromatic amines have been synthesized, among them hexamethyl-N-pentafluorophenyl-disilylamine.     

Reactions of Et(3)ZnLi with ketones: electronic and steric effects(1)

Toluene solutions of composition Et(3)ZnLi react rapidly with aldehydes and ketones to form addition products. Et(3)ZnNa and Et(3)ZnK solutions react readily with the same substrates although metalation, as well as addition, is significant with substrates having alpha-hydrogens. The Et(3)ZnM solutions react with 2-cyclohexenone to give mainly the 1,4-addition product. Relative rates of addition of Et(3)ZnLi to substituted acetophenones give a Hammett rho of 2.78. Addition of Et(3)ZnLi to acetophenone is slowed significantly by alpha and ortho methyl substituents; relative rates of addition to acetophenone, o-methylacetophenone, and tert-butyl phenyl ketone are 1.00, 0.012, and 0.003.     

Electronic and steric effects on the intramolecular Schmidt reaction of alkyl azides with secondary benzyl alcohols

The intramolecular Schmidt reaction of simple azido secondary benzyl alcohols has been realized for the first time. Investigation of the electronic and steric effects of the substrates on the product outcome was conducted. Unique intramolecular Schmidt rearrangements were observed with the formation of a cinnamaldehyde derivative and aryl aldehydes, respectively. Using this protocol, an efficient synthesis of dihydrobenzotriazine derivatives was achieved. Moreover, a practical approach to 2-aryl-1-pyrrolines was also accessed.     

Using mechanistic and computational studies to explain ligand effects in the palladium-catalyzed aerobic oxidation of alcohols

The experimental and computational mechanistic details of the Pd(OAc)(2)/TEA-catalyzed aerobic alcohol oxidation system are disclosed. Measurement of various kinetic isotope effects and the activation parameters as well as rate law derivation support rate-limiting deprotonation of the palladium-coordinated alcohol. Rate-limiting deprotonation of the alcohol is contrary to the majority of related kinetic studies for Pd-catalyzed aerobic oxidation of alcohols, which propose rate-limiting beta-hydride elimination. This difference in the rate-limiting step is supported by the computational model, which predicts the activation energy for deprotonation is 3 kcal/mol higher than the activation energy for beta-hydride elimination. The computational features of the similar Pd(OAc)(2)/pyridine system were also elucidated. Details of the study illustrate that the use of TEA results in an active catalyst that has only one ligand bound to the Pd, resulting in a significant lowering of the activation energy for beta-hydride elimination and, therefore, a catalyst that is active at room temperature.     

Steric effects in synthesis—steric limits to the alkylation of nitriles and carboxylic acids

The steric limits to the alkylation of aliphatic nitriles and carboxylic acids have been investigated in some detail. For the experimental conditions considered (ionization by i-Pr₂NLi in THF followed by alkylation with RI/THF/HMPA) the most hindered nitriles R-CN and carboxylic acids R-CO₂H have the same secondary alkyi group RtBuPⁱCH-, but different tertiary. i.e. Rt-BuPrⁱEtC- or i-Pr₃C- for RCN and REt₂MeC for RCO₂H. A comparison of the relative merits of alkylation of esters, carboxylic acids, and nitriles is considered.     

Diastereoselective addition of diethyl difluoromethylphosphonate to enantiopure sulfinimines: synthesis of α,α-difluoro-β-aminophosphonates, phosphonic acids, and phosphonamidic acids

Addition of diethyl lithiodifluoromethylphosphonate to enantiomerically pure aromatic, heteroaromatic, and aliphatic aldehyde-derived sulfinimines afforded N-sulfinyl α,α-difluoro-β-aminophosphonates with generally good enantioselectivity and in high yield. The reaction with acetophenone-derived sulfinimine resulted in the formation of the addition product with high diastereoselectivity and in only moderate yield. A two-step deprotection involving treatment of diastereomerically pure N-sulfinyl α,α-difluoro-β-aminophosphonates with trifluoroacetic acid in EtOH followed by refluxing with 10 N HCl provided enantiopure α,α-difluoro-β-aminophosphonates and α,α-difluoro-β-aminophosphonic acids. The N-Cbz derivative of (R)-2-amino-1,1-difluoro-2-phenylethylphosphonate was a convenient starting point for the preparation of corresponding difluorophosphonate monoester, difluorophosphonic acid, and difluorophosphonamidic acid. At 21 °C difluorophosphonamidic acid was stable in aqueous solution at pH above 5.     

Catalytic regioselective sulfonylation of alpha-chelatable alcohols: scope and mechanistic insight

This paper describes a convenient protocol for the regioselective sulfonylation of alpha-chelatable alcohols. Typically, the reaction of alpha-heterosubstituted alcohols with 1 equiv of p-TsCl and 1 equiv of Et(3)N in the presence of 2 mol % of Bu(2)SnO leads to rapid, regioselective, and exclusive monotosylation. The pK(a) of the amine was correlated to the reaction rate. A plausible mechanism for this reaction has been proposed on the basis of (119)Sn NMR studies.     

Reactions of trialkylsilanes with alcohols and carbonyl compounds,catalyzed by fluoride anion

Conclusions In anhydrous acetonitrile the ionic potassium, cesium and tetraethylammonium fluorides catalyze the reactions of trialkylsilanes with alcohols and carbonyl compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 932–934, April, 1973.     

Reactions of polyhalomethanes with olefins catalyzed by copper complexes with aromatic amino alcohols

Copper complexes with amino alcohols structurally similar to ephedrin (1-phenyl-3-(N-methylamino)propan-1-ol and 1-phenyl-2-(N-methylamino)ethanol) are catalytically very active in the free-radical addition of CCl₄ and CBr₄ to linear alk-1-enes. These amino alcohols themselves are initiators of radical addition reactions, and, in the reaction with CBr₄, they are more active than the metal complexes. In the presence of the amino alcohols, as distinct from classical radical initiators, the reaction is highly selective and affords an addition product. An analysis of kinetic equations and the data obtained for the reaction involving CHCl₃ suggest that the amino alcohols and the corresponding metal complexes are involved in different ways in the addition of CCl₄ and CBr₄ to linear alk-1-enes.     

Reactions of hydropolysilanes with alcohols catalysed by tris(triphenylphosphine)chlororhodium

[RhCl(PPh₃)₃] is a very effective catalyst for the cleavage of Si-Si bonds by alcohols.     

Iodine-promoted silylation of alcohols with silyl chlorides. Synthetic and mechanistic studies

An efficient silylating system for 1°, 2°, and 3° alcohols, consisting of a silyl chloride/N-methylimidazole/iodine, was developed. Synthetic and mechanistic aspects of this new reagent system, and particularly the role of iodine were investigated in detail using ¹H NMR spectroscopy.     

Phospha-Michael additions to activated internal alkenes: steric and electronic effects

The addition of P(O)-H bonds to internal alkenes has been accomplished under solvent-free conditions without the addition of a catalyst or radical initiator. Using a prototypical secondary phosphine oxide, a range of substrates including cinnamates, crotonates, coumarins, sulfones, and chalcones were successfully functionalized. Highly activated acceptors such as isopropylidenemalononitrile and ethyl 2-cyano-3-methyl-2-butenoate underwent the phospha-Michael reaction upon simple trituration of the reagents at room temperature, whereas less activated substrates such as ethyl cinnamate and methyl crotonate required heating (>150 °C) in a microwave reactor to achieve significant consumption of the starting alkenes. For the latter alkenes, a competing reaction involving disproportionation of the ditolylphosphine oxide into ditolylphosphinic acid and ditolylphosphine was observed at the high temperatures needed to promote the addition reaction.     

Reactions of 1-vinylbenzimidazole-2-thione with alcohols and phenol

1-(-Alkoxyethyl)- and 1-(-phenoxyethyl)benzimidazole-2-thiones were obtained in the reaction of 1-vinylbenzimidazole-2-thione with alcohols and phenol in the presence of gaseous hydrogen chloride. It was established that partial hydrolysis of the 1-(-alkoxyethyl)benzimidazole-2-thiones to benzimidazole-2-thione with subsequent alkylation with excess alcohol at the exocyclic sulfur atom occurs under the conditions of the investigated reaction. A convenient method for the alkylation of thiones was proposed, and a number of 2-alkylthiobenzimidazoles were synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 805–807, June, 1984.