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The microwave-assisted cyclocondensation of alkynones (I) with o-phenylenediamines (II) leads to desired 1,5-benzodiazepines (III) in good yields.

An effective, highly atom economical, and regioselective method for the synthesis of the title compounds is presented and requires no isolation of the hydrazone.

Synthesis of highly substituted 3-fluorofurans is reported. The sequence began with preparation of tert-butyldimethylsilyl alk-1-en-3-yn-1-yl ethers from 1,4-disubstituted alk-3-yn-1-ones. Subsequent fluorination of alkenynyl silyl ethers with Selectfluor gave 2-fluoroalk-3-yn-1-ones in almost quantitative yield. Subsequent 5-endo-dig cyclizations using chlorotriphenylphosphine gold(I)/silver trifluoromethanesulfonate (5/5 mol%), N-bromo- or N-iodosuccinimide and gold(I) chloride/zinc bromide (5/20 mol%), all at room temperature, provided a facile method for the generation of substituted 3-fluoro-, 3-bromo-4-fluoro-, and 3-fluoro-4-iodofurans in good yields. Also, 2,2-difluoroalk-3-yn-1-ones were prepared by fluorination of alk-3-yn-1-ones under organocatalytic conditions. The structures of (Z)-tert-butyldimethylsilyl but-1-en-3-yn-1-yl ether, 3-bromo-4-fluorofuran, and 3-fluoro-4-(phenylethynyl)furan were confirmed by X-ray crystallography.

Fluorination of enynol silyl ethers (I) and (III) generates title fluoroalkynones which smoothly undergo Au(I)—Zn(II)-catalyzed 5-endo-dig halocyclization with NIS or NBS to afford polysubstituted fluorohalofuran derivatives (II) and (IV), resp., in good overall yields.

Fluorination of substrates (I) with Selectfluor gives 2-mono-fluorobutynones (II) which undergo subsequent 5-endo-dig cyclization in the presence of a gold(I)-catalyst and silver triflate providing 2,5-diaryl-substituted 3-fluorofurans in high yields.

Reactions of 5-p-tolylethynyl-2′-deoxyuridine and 3′,5′-di-O-acetyl-5-p-tolylethynyl-2′-deoxyuridine with Co2(CO)8 in THF gave 5-p-tolC2[Co2(CO)6]-2′-deoxyuridine and 3′,5′-di-O-acetyl-5-p-tolC2[Co2(CO)6]-2′-deoxyuridine (92 and 66%).

Starting with 5-iodo-2'-deoxyuridine, a series of 5-alkynyl-2'-deoxyuridines (with n-propyl, cyclopropyl, 1-hydroxycyclohexyl, p-tolyl, p-tert-butylphenyl, p-pentylphenyl, and trimethylsilyl alkyne substituents) have been synthesized via the palladium-catalyzed (Sonogashira) coupling reaction followed by a simplified isolation protocol (76-94% yield). The cytotoxic activity of modified nucleosides against MCF-7 and MDA-MB-231 human breast cancer cells has been determined in vitro. 5-Ethynyl-2'-deoxyuridine, the only nucleoside in the series containing a terminal acetylene, is the most potent inhibitor with IC(50) (microM) 0.4+/-0.3 for MCF-7 and 4.4+/-0.4 for MDA-MB-231.

5-Endo-dig cycloisomerization of 1,4-di- and 1,2,4-trisubstituted but-3-yn-1-ones in the presence of a catalytic amount of zinc chloride (10 mol %) in dichloromethane at room temperature (22 °C) provides 2,5-di- and 2,3,5-trisubstituted furans in high yields (85−97%).

[reaction: see text] Thionation of amides, 1,4-diketones, N-(2-oxoalkyl)amides, N,N'-acylhydrazines, and acyl-protected uridines with the use of a fluorous analogue of the Lawesson's reagent leads to thioamides, thiophenes, 1,3-thiazoles, 1,3,4-thiadiazoles, and acyl-protected 4-thiouridines. The isolation of the final products in high yields is achieved in most cases by a simple filtration (fluorous solid-phase extraction).

Recent progress in synthetic approaches to the Mitsunobu reaction are reviewed. Efforts that have focused on the phase-switching modifications of phosphane, azodicarboxylate, and nucleophilic components are emphasized. An approach to product separation with fluorous compounds is reviewed in detail. Alternative reagents and recently introduced products are cited. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The remarkably selective reaction of O,O,O-dialkyltrimethylsilylselenophosphates (1) in the presence of equimolar amounts of dialkyltrimethylsilyl phosphites (2) with sulphuryl chloride leading to tetra-alkyl symmetrical selenopyrophosphates (3) in excellent yields is reported.