Copper-catalyzed rearrangement of vinyl oxiranes

A novel copper-catalyzed vinyl oxirane ring expansion protocol has been developed. A wide range of vinyl oxiranes can be rearranged to 2,5-dihydrofurans in excellent yields in the presence of electrophilic copper(II) acetylacetonate catalysts. Regioisomeric vinyl oxiranes can be converted to a single dihydrofuran product using these conditions. This method uses low catalyst loadings (0.5-5 mol %), has good tolerance of substitution patterns, and can be done in the absence of solvent.     

A novel rearrangement reaction. A single-step conversion of tetrahydro-1-isoquinolinecarboxylic acids into 1-isoquinolones

The preparation of 2-acyl-6,7-dimethoxy-1,2,3,4-tetrahydro-1-isoquinolinecarboxamides is described. The mixed anhydride of 2-acyl-6,7-dimethoxy-1,2,3,4-tetrahydro-1-isoquinolinecarboxylic acid with isobutyl chloroformate was reacted with the corresponding hydrazines at — 10, — 15°. Besides those compounds, isoquinolones occur through a new side reaction. The structure of those products was established by ¹³C and ¹H nmr and mass spectroscopy. A possible mechanism of the reaction is discussed.     

Superbase-promoted rearrangement of oxiranes to cyclopropanes

Aryl- and alkenyl substituted oxiranes, when submitted to treatment with superbasic reagents, undergo a highly regio- and stereoselective rearrangement leading to cyclopropylmethanol derivatives. The process can also be applied to mono- and dihydroxy substituted substrates thus leading to polyhydroxylated cyclopropanes.     

Rhenium complex-catalyzed Meinwald rearrangement reactions of oxiranes

The Meinwald rearrangement reaction of oxiranes to the corresponding carbonyl compounds is efficiently catalyzed by the ReBr(CO)₅ complex.     

A new heterocyclic rearrangement: conversion of 2-vinylpyrazolium salts into 1,2-dihydropyrimidines

Treatment of 2-vinylpyrazolium salt $\text{1}$ in basic medium yields the 1,2-dihydropyrimidine $\text{2}$. The structure of $\text{2}$ was established by analytical and spectroscopic methods.     

The acid catalysed rearrangement of a diterpenoid epoxide

A study has been made of the principal rearrangement products resulting from formic acid treatment of 19-hydroxy-ent-beyerene epoxide (3). In concentrated solutions 3 has been found to undergo a deep seated rearrangement to the allylic alcohol (14). A mechanism for the formation of 14 is proposed involving a novel 1,4-hydride shift in the bicyclo[3:2:1]octane C/D ring system following cleavage of the C₁₅O bond. Supporting evidence has been obtained from a study of the specifically labelled epoxide (4), the deuterium in 14 appearing exclusively at C₁₂. Four products (7 and 11–13) emanating from the known beyerane → kaurane interconversion have been identified.     

The conversion of azobenzenes to phenazines: A new molecular rearrangement

When azobenzenes arc heated with ferrous oxalate or with a fused mixture of aluminum chloride and sodium chloride the corresponding phenazines are formed in low yield. Azobenzene itself is exceptional in giving benz[c]cinnoline with AlCl₃-NaCl. Azoxybenzenes and ferrous oxalate give azobenzenes and some phenazines, while azoxybenzene itself also gives 2-hydroxyazobenzene via a Wallach-type rearrangement. The rearrangements are thought to occur at the surfaces of the reagent. No rearrangement to the phenazines occurs in the absence of the reagent.     

A novel rearrangement of eudesmanolide enol ester epoxide: facile 1-step construction of the salvialane sesquiterpene skeleton

A novel carbon–carbon rearrangement for the eudesmanolide sesquiterpene enol ester epoxide in the presence of a catalytic amount of Lewis acids (3–10 mol%) or an excess of NaOMe is disclosed. This reaction was developed to give a facile, one-step procedure for the construction of naturally occurring and bioactive salvialane sesquiterpenes. The reaction conditions were investigated extensively and a possible reaction mechanism is also discussed.     

A novel titanium-catalyzed cyclization of olefinic iodoethers to tetrahydrofurans

A catalytic reductive cyclization of olefinic iodoethers was achieved by use of cat. Cp(2)TiCl(2) in the presence of Mn and Me(3)SiCl. This protocol provides a versatile method for the selective formation of multisubstituted tetrahydrofurans.     

The carbonyl epoxide rearrangement. A chiral synthesis of the mus musculus pheromone

The carbonyl-epoxide rearrangement in conjunction with the Sharpless asymmetric epoxidation procedure has been applied to an efficient synthesis of both enantiomers corresponding to the Mus musculus pheromone.     

A novel oxamide rearrangement

An efficient, base-induced rearrangement of 2-[(1,2-dioxo-2-(methylamino)ethyl)phenylamino]benzoic acid methyl ester ( 7a ) to the isomeric 2-[(1,2-dioxo-2-(phenylamino)ethyl)methylamino]benzoic acid methyl ester ( 27a ) is described. This novel rearrangement must proceed through a spiro intermediate wherein benzoate is acting as a Michael receptor. When 2-[(1,2-dioxo-2-(methylamino)ethyl)methylamino]benzoic acid methyl ester ( 28 )-an oxamide which would produce a degenerate spiro intermediate — was subjected to rearrangement conditions, the product obtained was 1,3-dimethyl-2,4-(1H,3H)quinazolinedione ( 29 ). This latter transformation may have proceeded via a benzodiazepinetrione intermediate.     

Acid catalyzed rearrangement of β-ionone epoxide

Rearrangement of β-ionone epoxide with aqueous formic acid gave 1,2-dihydro-1,1,6-trimethylnaphthalen (2), 1-(1,2,2-trimethylcyclopent-1-yl)-2-penten-1,4-dione (3), 4-(5,5-dimethyl-2-acetyl-1-cyclopenten-1-yl)-2-butanone (5), 4-(1,3,3-trimethyl-2-cyclohexanon-1-yl)-3-buten-2-one (6), 4-(2,3,6-trimethylphenyl)-2-butanone (7) and 6,6-dimethyl-2,5-10-undecatrione (8). NMR assignments are made for each compound while a computer assisted analysis of the A₂B₂ portion of 7 has been completed. Possible mechanistic pathways leading to these compounds are discussed.     

New rearrangement of 4-isoxazoline system: conversion of ketones into alpha,beta-unsaturated amides

A new rearrangement pattern of the 4-isoxazoline system is reported. The reaction, starting from 3,3-disubstituted derivatives and leading to alpha,beta-unsaturated amides, proceeds through the quaternarization of the nitrogen atom and involves the heterolytic cleavage of C(3)-N bond, assisted by the formation of a relatively stable intermediate. The overall process represents a useful conversion of ketones into alpha,beta-unsaturated amides.     

A novel acid-catalyzed rearrangement of cyclobutanols

Under acid-catalysis 7-arylbicyclo[3.2.0]hept-2-en-6-ols rearrange to diarylmethanes and cyclopenteno-annelated polycyclic aromatic hydrocarbons.     

A novel conversion of acetylenic 1,2,4-triazoles into 3-alkyl-5-arylpyridazines

Bromination of 2-aryl-1-[1,2,4]triazol-1-ylalk-3-yn-2-ols gives 6-bromo-7-hydroxy-5-alkyl-7-aryl-7,8-dihydro-[1,2,4]triazolo[1,2-a]pyridazin-4-ylium salts, which are converted by treatment with strong alkali into novel 3-alkyl-5-arylpyridazines.     

A novel asymmetric vinylogous tin-Pummerer rearrangement

A new type of vinylogous tin-Pummerer rearrangement reaction was observed when benzyl tin derivatives containing a sulfinyl group at the ortho position were allowed to react with acyl chlorides or TFAA. The reaction is thought to proceed by nucleophilic attack of the leaving carboxylate at the gamma-position of the conjugated thionium ion. The enantioselectivity (ee) of the reaction can reach values as high as 98%. The observed stereoselectivity is related to the nature of the solvent, the temperature employed, and the stability of the migrating carboxylate anion. [reaction--see text]