1.3- Dioxanes reactions, review

The Lewis acid-catalyzed reaction of 4-acetoxy-l,3-dioxanes with nucleophiles has been reviewed <2001TCC(216)51>. The principles of the reaction are displayed in (Equation 44). The combination of boron trifluoride and organozinc compounds was found to be very efficient <1997JOC6460, 1999JOC2026> but allylsilanes react as well <19%SL536, 1998TL6811>. 

Photocycloadditions of naphthalene derivatives to alkcnes have been recently reviewed.60 Examples of such reactions are the photocycloaddition of naphthalene to 2,3-dihy-drofuran,61 of 4-methoxy-l-naphthonitrile to acrylonitrile62 and of 2-trimethylsiloxynaph-thalene to methyl acrylate.63 2-Naphthols undergo cycloaddition with ethene in the presence of aluminum trihalides only.64 Other bicyclic aromatic compounds, e.g. A-acylindoles65-67 and /V-methylphenanthrene-9,10-dicarboximide,68 have also been studied in detail. Irradiation of 5/f-dibenzo[u,i7]cyclohepten-5-one (21) and dimethyl 2-methylfumarate (22) in dioxane gives the cyclobutane adduct 23 in 73% yield.69... 

The synthesis of poly(vinyl acetals) (252) represents another example of generating a heterocycle, in this case the 1,3-dioxane nucleus, by application of a polymer modification reaction. Generally, the polymer modified is poly(vinyl alcohol) (180) or one of its copolymers. The 1,3-dioxane ring is generated (Scheme 122) by an acid-catalyzed acetalization reaction with an aldehyde, although ketones have also been reacted. A review (71MI11102) is available covering synthesis, properties and applications of the two most common and industrially important poly(vinyl acetals), poly(vinyl butyral) and poly(vinyl formal), as well as many other functional aldehydes that have been attached. 

Data have been presented on the kinetics of nitration of acetanilide in mixtures of nitric and sulfuric acids.29 A review discusses the several mechanisms operative in the nitration of phenol including /> / -sclective nitrosation-oxidation and mechanisms involving phenoxy radical-nitrogen dioxide reaction yielding a 55 45 ortho para nitration ratio.30 The kinetics of mononitration of biphenyl-2-carboxylic acid have been investigated in several solvents. The maximum ortho para product ratio of 8.4 is observed in tetrachloromethane.31 Nitration products were not formed in the presence of dioxane.31,32 Quantum-chemical AMI calculations were performed and the predominant formation of the ortho-nitro product is accounted for by stabilization of the cr-complex by the carboxyl group.33... 

Quantum mechanical calculations show that the silyl cation (19) has a twisted structure, and that the a-C02 group provides substantial electrostatic stabilization.58 Isotope effects for its formation reaction are also reported.58 Evidence is provided for the stabilization of incipient oxocarbenium ions by axial electronegative substituents, as in (20) the presence of the most electronegative substituent results in the fastest reaction.59 Lewis acid-promoted cleavage of spirocyclic dioxanes such as (21) involves oxonium ions, and high axial vs equatorial product selectivities are possible with the correct choice of Lewis acid and nucleophile.60 Reactions which lead to 1,3-dioxenium salts have been reviewed.61... 

In a review of nucleophile isotope effects in chemistry, the hydrolysis of formates was discussed.10 The effect of dioxane on the acid-catalysed hydrolysis of ethyl formate was studied by carrying out the reaction in 0-80% (v/v) dioxane at different temperatures ranging from 20 to 40 °C. It was proposed that up to 1.5 mol of water are associated with the activated complex.11 Kinetic studies of the alkaline hydrolysis of ethyl decanoate12 in DMF-H2O solutions and of ethyl isovalerate13 in aqueous acetone were reported. 

Very similar results are obtained in Cdl30JT-H20, dioxane-lLjO, and C>Il60H-IT20 mixtures and in pure IICOOH as well. A. Streitweiser, Jr., Chem. lievs, 56, 571, 620 (1966) (see his Fig. 14), has presented a veiy comprehensive review of the kinetics of displacement reactions. 

An extensive study of the reduction of 2.4,6-trinilrotoIuene was made by Nielsen. Coon and co-workers (55. They also reviewed the existing literature. So far the use of different reducing agents produced mainly 4-amino-2.0-dinitro-tolucnc. Nielsen. Coon et tfC. examined the use ofhydrogen sulphide in the presence of a catalytic amount of ammonia and found the reaction to be solvent dependent in dioxane both 4-amino 2.6- and 2-ainino-4.6-dinitroto uenes being... 

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