A systematic study of the reaction of β-hydroxy ethers with ruthenium tetraoxide (RuO4), generated in situ from ruthenium trichloride and sodium periodate, is presented, leading to nine-membered ring keto-lactones in moderate yields. Three different solvent systems - AcOEt/MeCN/H2O, MeCN/H2O and DMC/H2O - were studied leading to the desired products in lower yields than those obtained with the classical mixture of CCl4/MeCN/H2O, commonly used in reactions promoted by this oxidant. However, it is noteworthy that these new solvent systems represent greener alternatives to the chlorinated solvents used in the oxidative cleavage of β-hydroxy ethers by RuO4.

The reaction of ten cis-octalins and cis-octalones with thallium trinitrate (TTN) leads to different products, depending mainly on the substitution pattern of the substrate. Functionalized cis-hydrindanes were obtained from the reaction of 1,2,3,4,4a,5,8,8a-octahydro-4a-methylnaphthalene and of 1,2,3,4,4a,5,8,8a-octahydro-4a,7-dimethylnaphthalene with TTN in acetonitrile, whereas a cyclic ether was formed treating 1,2,3,4,4a,5,8,8a-octahydro-6,8a-dimethylnaphthalen-1-ol with TTN in trimethylorthoformate (TMOF).

The bioreduction of a series of substituted a-tetralones, carried out using Daucus carota root (carrot), afforded the corresponding homochiral a-tetralols in variable conversions (9 to 90%) and excellent enantiomeric excesses. Two of the assayed a-tetralones were resistant to the bioreduction conditions. The absolute configurations of four a-tetralols were assigned as being (S), by comparison to the (S)-enantiomers obtained by kinetic resolution promoted by CALB-catalysed acetylation. Additionally, the new 5-methoxy-6-methyl-1-tetralone was synthesized in seven steps from 3-methylsalicylic acid.

The natural occurrence, biological activities and synthetic approaches to natural eight-, nine-, and eleven-membered lactones is reviewed. These medium ring lactones are grouped according to ring size, and their syntheses are discussed. The structures of some natural products early identified as medium-ring lactones were revised after total synthesis.

Enaminones are beta-enamino carbonylic compounds bearing the conjugated system N-C=C-C=O, which makes them versatile ambident synthetic building blocks, particularly in synthesis of heterocycles. This review covers the last three years of the literature concerning the preparation and synthetic applications of enaminones.

There are several natural products bearing medium ring lactone moieties, which are those containing a ring size in the range of 8 to 11 members. This review intends to cover the last 10 years (1996-2005) of the literature concerning the synthesis of medium ring lactones.

A oxidação de álcoois homoalílicos terciários com trinitrato de tálio (TTN) foi investigada. Os álcoois que possuem uma metila na posição alílica perdem uma molécula de acetona via uma reação de fragmentação, levando a uma mistura de álcoois alílicos isoméricos como principais produtos, juntamente com os correspondentes derivados acetilados. Por outro lado, o tratamento com TTN de álcoois terciários análogos, sem a metila na posição alílica, fornece indanos, através de uma reação de contração de anel.

The oxidation of tertiary homoallylic alcohols with thallium trinitrate (TTN) was investigated. The alcohols bearing an allylic methyl group lose a molecule of acetone via a fragmentation reaction that leads to isomeric secondary allylic alcohols as major products, together with their corresponding acetylated derivatives. On the other hand, treating analogous tertiary alcohols without the allylic methyl group with TTN gives indans, through a ring contraction reaction.

O rearranjo de ésteres beta,gama-insaturados, tais como 2-(3,4-di-hidronaftalen-1-il)-propionato de etila, com trinitrato de tálio (TTN) em ácido acético leva a 3-indan-1-il-2-metil-3-oxo-propionatos de etila com bom rendimento, através de uma reação de contração de anel. Os novos indanos assim obtidos possuem uma unidade beta-ceto éster, a qual pode ser útil para transformações posteriores.

The rearrangement of beta,gamma-unsaturated esters, such as 2-(3,4-dihydronaphthalen-1-yl)-propionic acid ethyl ester, with thallium trinitrate (TTN) in acetic acid leads to 3-indan-1-yl-2-methyl-3-oxo-propionic acid ethyl ester in good yield, through a ring contraction reaction. The new indans thus obtained feature a beta-keto ester moiety, which would be useful for further functionalization.

A oxidação de uma série de 1,2-diidronaftalenos, substituídos no anel aromático, foi investigada com trinitrato de tálio (TTN) em metanol ou em trimetilortoformiato (TMOF) como solvente. Em todos os casos, indanos foram formados, embora o rendimento tenha variado de excelente a baixo, dependendo da estrutura do substrato. A presença de um grupo doador de elétrons no substrato favorece o rearranjo, enquanto que uma quantidade significativa de derivados glicólicos, bem como naftalenos, foi obtida na oxidação de 1,2-diidronaftalenos com um grupo retirador de elétrons, tais como Br e NO2. Mecanismos para a formação de cada um destes produtos foram propostos.

The oxidation of a series of 1,2-dihydronaphthalenes substituted in the aromatic ring was investigated with thallium trinitrate (TTN) in methanol or in trimethylorthoformate (TMOF) as solvent. In all cases, indans are produced, although the yield varied from excellent to poor, depending on the structure of the substrate. The presence of an electron-donating group in the substrate favors the rearrangement, whereas significant amounts of glycolic derivatives, as well as naphthalenes, were obtained in the oxidation of 1,2-dihydronaphthalenes bearing electron-withdrawing groups, such as Br and NO2. Mechanisms for the formation of each of these products are proposed.

Este trabalho descreve a reação de desidroiodação, promovida por base, de uma série de beta-iodo-enol éteres cíclicos. Os produtos são tetraidrofuranos contendo duas ligações duplas exocíclicas, di- e tetraidrobenzofuranos e um derivado de diidropirano, todos obtidos em ótimos rendimentos.

This work describes the base-promoted dehydroiodination of differently substituted cyclic beta-iodo-enol ethers. The products are tetrahydrofuran derivatives bearing two exocyclic double bonds, di- and tetrahydrobenzofurans and a dihydropyran derivative, which were obtained in very good yields.

The indan ring system is present in several compounds with important pharmacological properties. In this account recent examples of selected methods (Friedel-Crafts acylation, cycloaddition reactions, ring contraction, cyclization and resolution) for the synthesis of indans are discussed.

The general term "enaminone" is applied to any compound bearing the conjugated system N-C=C-C=O. Enaminones are typical capto-dative ethylenes, showing particular properties due to pi-electron delocalization. Their reactivity can be predicted by structural patterns of substitution, conformation and configuration, making them versatile synthetic building blocks. In this review, a variety of methods for the synthesis of enaminones is described. The methods were divided into condensation of amines to beta-dicarbonyl compounds, addition of amines to <FONT FACE=Symbol>a,b</FONT>-unsaturated carbonyl compounds, condensation between carbonyl compounds and N-unsaturated functions and other methods, covering the period from 1993 to 2001.

A reação de uma série de 1-tetralonas com trinitrato de tálio adsorvido em Montmorilonita K-10 forneceu produtos de contração de anel (1-indanocarboxilatos de metila) e/ou alfa-oxidação (2-metóxi-1-tetralonas), em rendimentos bastante variáveis.

The reaction of a series of 1-tetralones with thallium trinitrate supported on Montmorillonite K-10 clay led to products of ring contraction (methyl indan-1-carboxylates) and/or alpha-oxidation (2-methoxy-1-tetralones), in variable yields.

A reação de uma série de cis-2-decalonas com TTN em CH2Cl2 à temperatura ambiente foi investigada. As reações de contração de anel ocorreram com bons rendimentos, porém a regio- e a diastereosseletividade foram baixas. A influência de grupos alquílicos na regioquímica da reação depende da sua posição no anel decalínico.

The reaction of some cis-2-decalones with TTN in CH2Cl2 at room temperature was investigated. The ring contraction reactions occurred in good yields, however the regio- and diastereoselectivity were low. The effect of the alkyl groups in the regiochemistry of the reaction depends on their position at the decalone ring system.

Thallium(III) salts promote a number of different reactions useful in organic synthesis. In this paper, the ring contraction of ketones and olefins, mediated by thallium(III) salts, is exhaustively reviewed.