Rearrangements titanium chloride

In a study of the reaction of the anomeric forms of penta-O-acetyl-D-glucopyranose with titanium chloride in chloroform solution, Lemieux and Brice have found that, at 40°, the a-D anomer reacts but slowly, whereas the /3-d anomer reacts extremely rapidly, with the initial formation of (unstable) tetra-0-acetyl- S-D-glucopyranosyl chloride which then rearranges relatively slowly to (stable) tetra-O-acetyl-a-D-glucopyranosyl chloride. 

As catalysts for the Fries rearrangement reaction are for example used aluminum halides, zinc chloride, titanium tetrachloride, boron trifluoride and trifluoromethanesulfonic acid7... 

Synthesis of the remaining half of the molecule starts with the formation of the monomethyl ether (9) from orcinol (8). The carbon atom that is to serve as the bridge is introduced as an aldehyde by formylation with zinc cyanide and hydrochloric acid (10). The phenol is then protected as the acetate. Successive oxidation and treatment with thionyl chloride affords the protected acid chloride (11). Acylation of the free phenol group in 7 by means of 11 affords the ester, 12. The ester is then rearranged by an ortho-Fries reaction (catalyzed by either titanium... 

The formation of the isocorrolecarbaldehyde 5 may be best explained if one invokes 1,2-diol 4 as an intermediate of the McMurry coupling which would then react in a titanium(IV) chloride induced Wagner-Meerwein rearrangement to yield the isocorrole 5 as a minor product during... 

Aluminum trichloride is the most commonly used catalyst, although aluminum tribromide is more efficient.1 For the rearrangement of l-broino-2-chloro-1,L2-lrifluoroethane (3) to 2-bromo-2-chloro-l,l,l-trifhioroethane (4). none of the following Lewis acids are effective iron(III) chloride. iron(III) bromide, antimony(III) chloride, antimony(V) chloride. tin(IV) chloride, titanium(IV) chloride, zinc(II) chloride, and boron trifluoride-diethyl ether complex.1" ... 

CLAISEN REARRANGEMENT Alkylaluminum halides. Lithium diisopropylamide. Potassium hydride. Sodium dithionite. Titanium(TV) chloride. Trifluoroacetic acid. Trimethylaluminum. 

By using a stoichiometric amount of the chiral titanium reagent prepared by mixing chiral diol, Titanium IV) Chloride, and titanium tetraisopropoxide, the asymmetric [2 + 2] cycloaddition reaction of 1,4-benzoquinones and styrenes gives the corresponding cyclobutane derivatives with high optical purity. These rearrange to 2,3-dihydrobenzofuran derivatives on mild acid treatment (eq 13). ... 

Pacsu and CrameF treated a chloroform solution of hexaacetylmaltose methyl 1,2-orthoacetate with titanium tetrachloride and obtained the normal heptaacetyl-a-maltosyl chloride. In like manner, when dry hydrogen bromide in glacial acetic acid was employed, a rapid formation of the normal heptaacetyl-a-maltosyl bromide resulted. Obviously, the replacement of the methoxyl group of the methyl orthoacetate by a halogen atom was accompanied by a rearrangement of the orthoester... 

A stereochemical control of the Ugi reaction can be effected with carbohydrates as chiral templates (e.g. tetrakis(O-pivaloyl)galactosylamine), which gives rise to easily separable amides. From these a variety of non-natural amino acids can be derived after acidic hydrolysis. The Passerini reaction, related to the Ugi rearrangement, gives a-hydroxyamides. A modification of this reaction using titanium tetrachloride gives a-branched amides in high yields via C-metalated imidoyl chlorides (equation 38). 

Taub et ai at Merck used titanium tetrachloride to effect rearrangement of the phenol ester (1) to the benzophenone (2). In this case use of aluminum chloride led mainly to fragmentation into the components and the best yield of (2) was 5%. 

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