Stereospecific palladium-catalyzed cross-coupling of (E)- and (Z)-alkenylsilanolates with aryl chlorides

The cross-coupling of geometrically defined (E)- and (Z)-alkenyl- and styrylsilanolates with a wide variety of aromatic and heteroaromatic chlorides has been achieved. Under catalysis by bulky, biphenyl-derived phosphines and allylpalladium chloride, the (preformed, stable) potassium salts of di-, tri- and tetrasubstituted alkenyldimethylsilanols undergo high yielding and highly stereospecific coupling to aryl chlorides in THF or dioxane. A variety of functional groups are compatible with these reaction conditions including nitro, ester, ketone, and nitrile. Both (E)- and (Z)-alkenylsilanolates coupled with nearly identical rate and efficiency.

Synthesis of 3,4,5-trisubstituted isoxazoles via sequential [3 + 2] cycloaddition/silicon-based cross-coupling reactions

[reaction: see text] A [3 + 2] cycloaddition reaction between alkynyldimethylsilyl ethers and aryl and alkyl nitrile oxides to produce isoxazolylsilanols has been developed. The cross-coupling reactions of these heterocyclic silanols with a variety of aryl iodides affords 3,4,5-trisubstituted isoxazoles. This sequential process allows for rapid variation of substituents at the 3, 4, and 5 positions of the isoxazole.

Palladium-catalyzed silylation of aryl bromides leading to functionalized aryldimethylsilanols

[reaction: see text] A mild and general palladium-catalyzed insertion of 1,2-diethoxy-1,1,2,2-tetramethyldisilane into a variety of aryl bromides affords the aryldimethylsilyl ethers in high yields. Hydrolysis of the ethers under pH-optimized conditions results in the exclusive formation of the desired aryldimethylsilanols.

Photochemical synthesis of aldehydes in the solid phase

A substituted anthraquinone (AQ), previously shown to photochemically generate benzaldehyde in methanol solution, was attached to a commercially available resin via an 11 carbon tether and an amide bond. Photolysis of the polymer-bound AQ with visible or 350 nm UV light resulted in the formation of benzaldehyde in yields of 50-55% as determined by HPLC. The phenolic positions in the polymer were then alkylated using benzyl bromide and 1-iodo-3-(4-nitrophenyl)propane in a coupling reaction with K(2)CO(3) as a base and a solution-phase proton shuttle. Photolysis of these alkylated polymers resulted in the formation of benzaldehyde (54-89%) and 3-(4-nitrophenyl)-propanal (58-67%). The yields of both aldehydes dropped considerably with subsequent realkylation and photolysis, and the polymer beads began to show signs of deterioration. This is the first time that aldehydes have been made photochemically on a solid-supported phase.