Catalytic alkynylation of diverse ketones and aldehydes using nonmetallic benzyltrimethylammonium hydroxide or a basic resin of the hydroxide type in DMSO is described. Aliphatic or alicyclic carbonyl partners gave satisfactory results, whereas aromatic ones afforded products with low yields. When aromatic aldehydes were reacted with phenylacetylene, enones such as chalcone derivatives were obtained in place of ynols. These organobase-catalyzed systems provide a practical nonmetallic protocol for C[bond]C formation.

Highly useful carbon-carbon bond forming reactions using stable allenyl, propargyl, or allyl-propargyl hybrid cations have been developed. These carbocations could be generated from silyl 1-(pi-donor)-substituted propargyl ethers by the action of trimethylsilyl trifluoromethanesulfonate in dichloromethane at -78 degrees C to room temperature and could be attacked nucleophilically by electron rich arenes, allylsilanes, or enol silyl ethers, giving rise to allenes, alkynes, and their derivatives. A novel method for regio- and stereoselective synthesis of conjugated enynes utilizing allyl-propargyl hybrid cations has also been established.

An efficient method for synthesizing 1-({[(3R,3aS,6aR)-hexahydrofuro­[2,3-b]­furan-3-yloxy]­carbonyl}­oxy)­pyrrolidine-2,5-dione (1), a key building block for HIV protease inhibitors, has been developed. A diphenylprolinol-catalyzed highly enantio- and diastereoselective cross aldol reaction of polymeric ethyl glyoxylate with an aldehyde was used as the key step. Acetalized aldol adduct was reduced with NaBH4 to give the diol intermediate in quantitative yield. The acetal exchange reaction followed by hydrogenation with Pd/C catalyst afforded 1′ in 95% yield over 2 steps. The condensation of 1′ with a carbonate gave crystalline 1 (>99/1 dr, > 99% ee) after single crystallization. This is a highly practical synthetic method since environmentally benign organocatalysis is utilized, the amount of catalyst is reduced to 3 mol %, and all of the intermediates before 1′ can be used without any purification.

[reaction: see text] This paper describes a novel method to synthesize a quinoline backbone by incorporating allenyl cations into a catalytic intramolecular Friedel-Crafts reaction. The initial products were isomerized and aromatized upon treatment with acid and base, respectively, to give quinolines. The basic concept also proved to be promising for 1-benzazepine, 1-benzazocine, or isoquinoline synthesis.

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