Current Organic Chemistry - Volume 7, Issue 2, 2003

Syntheses and reactions of β-carbonylallylsilane, conjugated allylsilane with a carbonyl group at the β-position, or its equivalent are reviewed. The method of the preparation of this moiety can be classified into (1) the introduction of silyl group at the allylic position of α,β-unsaturated carbonyl compounds, (2) carbonylation of allylsilane at the β-position, (3) elimination from pre-constructed β- silyl carbonyl compounds, (4) The Horner-Wadsworth-Emmons coupling reaction, and (5) others. β-Carbonylallylsilane can formally react with both an electrophile and a nucleophile at the same carbon, which makes it easy to synthesize odd membered cyclic compounds, such as five or seven-membered carbocycles related to terpenoids. The reaction of this unit with C=O or C=C produces γ-lactone or cyclopentane, respectively. The Nazarov cyclization of α-(trimethylsilylmethyl)divinyl ketones and the self-cyclization of 2-(trimethylsilylmethyl)pentadienal also provide new entries to five-membered carbocycle. The homo-Diels- Alder reaction and the homo-Cope rearrangement are developed using β-(hydroxymethyl)allylsilane derivatives as the carbon 1,3-dipole.

Recently, alkylation, alkenylation, and arylation of 4-cyclopentene-1,3-diol monoacetate have been published to produce 4-substituted-2-cyclopenten-1-ols (1,4- isomers) or 2-substituted-3-cyclopenten-1-ols (1,2-isomers). The product selectivity is usually high, and hence the products will provide a new access to the cyclopentanoids. This review describes scope and limitation of these reactions, synthetic advantages, comparison with the previous methods which also afford the same type of products indirectly or by using different substrates. In the latter part of this review, application of these reactions to synthesis of 12-oxo-PDA, OPC-8:0, Δ7-PGA1 methyl ester, the primary PG intermediates are presented.

The pyrazino[2,1-b]quinazoline-3,6-dione system is the key structural fragment of a group of alkaloids. The synthesis of derivatives of this system has been accomplished by means of three kinds of methods, starting from 4(3H)-quinazolinones, 2,5-piperazinediones or open-chain tripeptides, where anthranilic acid can be at the C-terminal, the N-terminal or the intermediate position of the tripeptide. Regarding its reactivity, much work has been developed to show that the system behaves as a glycine template. Thus, its C-1 position can be deprotonated by strong bases, and the anion thus generated undergoes stereoselective alkylations, acylations and Michael reactions. Hypervalent iodine reagents commonly employed for the α-functionalization of ketones also react at C-1, leading to electrophilic species that can be arylated and therefore used as precursors to polycyclic derivatives. Oxidation and Mannich reactions also occur at the C-1 position and lead to precursors of tertiary iminium cations. Some rearrangement reactions have been described, including a pyrazine-pyridine transformation and a transannular rearrangement that has ben proposed to explain some reactivity results. The aromatic ring of pyrazino[2,1-b]quinazoline-3,6-diones can be easily hydrogenated to give tetrahydro derivatives.

Though sulfur-containing heterocyclic compound syntheses have been extensively studied, syntheses of selenium analogues have not been appreciably investigated. Recently, however, reports of selenium-containing heterocyclic compound synthesis have gradually increased not only because of their interesting reactivities but also because of their pharmaceutical applications. For example, 1,3-selenazines showed significant anti-bacterial activity against both Gram-negative and Gram-positive bacteria and potential anti-tumor effects against several kinds of human cancer cell lines. Selenazofurin (2-β-D-ribofuranosylselenazole-4-carboxamide) demonstrated significant anti-tumor properties in animals and broad spectrum antiviral activity in cell culture experiments. Selenoureas and selenoamides have been used as the precursors for the most of the syntheses of 1,3-selenazines and 1,3-selenazoles. This review article summarizes the recent progress in the development of the synthesis methods of 1,3-selenazine and 1,3-selenazole and their biological significances.

Phthalocyanines exhibit a number of unique properties that make them of great interest in different scientific and technological areas. One of the most promising fields is the use of metallo phthalocyanine derivatives as photosensitizers for Photodynamic Therapy (PDT). Using PDT against cancer involves the irradiation of tumors with visible light following selective uptake of a photosensitizer by the tumor tissue. This review briefly summarizes the photophysical, photochemical and synthetic aspects of phthalocyanines compounds, evaluating their application for PDT.