Epoxides acid-catalyzed ring

Predict which carbon undergoes nucleophilic attack on acid catalyzed ring opening of cis 3 3 3 tnfluoro 2 3 epoxybutane Examine the C—O bond distances of the protonated form of the epoxide on Learning By Modeling How do these bond distances compare with your prediction" ... 

Maltol. Otsuka Chemical Co. in Japan has operated several electroorganic processes on a small commercial scale. It has used plate and frame and aimular cells at currents in the range of 4500—6000 A (133). The process for the synthesis of maltol [118-71 -8], a food additive and flavor enhancer, starts from furfural [98-01-1] (see Food additives Flavors and spices). The electrochemical step is the oxidation of a-methylfurfural to give a cycHc acetal. The remaining reaction sequence is acid-catalyzed ring expansion, epoxidation with hydrogen peroxide, and then acid-catalyzed rearrangement to yield maltol, ie ... 

Acid-catalyzed ring opening of epoxides is discussed in Section 16.13. 

Under some circumstances, acid-catalyzed ring opening of 2,2-disubstituted epoxides by sulfuric acid in dioxane goes with high inversion at the tertiary center.116... 

If the epoxide is unsymmetrical, the nucleophile attacks primarily at the more substituted carbon atom in acid-catalyzed ring opening. 

Cyelobutanone has been prepared by (1) reaction of diazomethane with ketene,4 (2) treatment of methylenecyclobutane with performic acid, followed by cleavage of the resulting glycol with lead tetraacetate,s (3) ozonolysis of methylenecyclobutane, (4) epoxidation of methylene-cyclopropane followed by acid-catalyzed ring expansion,7 and (5) oxidative cleavage of cyclobutane trimethylene thioketal, which in turn is prepared from 2-(co-chloropropyl)-l,3-dithiane.8... 

Nichols and co-workersstudied the formation of j8-hydroxy nitrate esters via the acid-catalyzed ring-opening of epoxides with nitrate anion. Reactions were conducted in aqueous media using solutions of ammonium nitrate is nitric acid and under nonaqueous conditions using solutions of pure nitric acid in chloroform. 2-Nitratoethanol (32) is formed in 58 % yield from ethylene oxide (30) using either of these methods. ... 

The ethylene glycol, bp 198°C, is readily vacuum distilled and separated from the DEG, bp 246°C, and TEG, bp 288°C. The mechanism of the reaction follows the general scheme for acid-catalyzed ring openings of epoxides. 

Diaryl-2-hydroxypropiophenones (607) are obtained from 4-hydroxychalcone and a reactive phenol on treatment with alkaline hydrogen peroxide in an epoxide-mediated coupling reaction. The ketones undergo a base-catalyzed a-ketol rearrangement to the isomeric l-hydroxypropan-2-ones (608) and acid-catalyzed ring closure provides a route to 4-arylflavan-3-ones (Scheme 231) (80JCS(Pl)1025). 

Summary Epoxide Syntheses 648 14-12 Acid-Catalyzed Ring Opening of Epoxides 649... 

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