Boronic acid-containing cyclic

The mechanism we have proposed to explain boronic acid-catalyzed amidation is depicted in Sch. 2. Arylboronic acid usually contains different amounts of cyclic tri-meric anhydrides (boroxines). The rate-determining step is the generation of ArB (OCOR)(OH). 

Hydroxy-3-alkylcyclopent-2-ene-l-ones. The substances (2) are available in 50-70% yield by treatment of 2,3-epoxy-2-alkylcyclopentanones (1, obtained by alkaline epoxidation of 2-alkylcyclopent-2-ene-l-ones) with acetic acid containing 2% of concentrated sulfuric acid at 55°. Use of boron trifluoride etherate, the classical reagent for rearrangement of cyclic 2,3-epoxy ketones (1,... 

The matter of purity is of real importance for SPC and should therefore be addressed. As boron-based functional groups, free boronic acid or one of the many cyclic boronic esters are used. The latter esters may hydrolyze to the acids during polymerization, which then enter the normal cross-coupling or follow an independent mecha-nism.f " Boronic acids always contain some water. Otherwise they are partially or completely condensed to cyclic boroxines. This water content has to be precisely... 

Heinrichs G, Schellentrager M, Kubik S (2006) An enantioselective fluorescence sensor for glucose based rai a cyclic tetrapeptide containing two boronic acid binding sites. Eur J Org Chem 18 4177-4186... 

The principle relies on the formation of cyclic esters between boronate ligands and 1,2- or l,3-ds-diol moieties to form five- or six-membered cyclic esters under alkaline pH conditions and the dissociation of the cyclic esters when the environmental pH is changed to acidic or a ds-di-ol-containing compound with higher affinity is added to the surrounding solution. The general formula of the reaction between boronic acids and... 

The Ma group has reported some very elegant multibond forming processes to synthesize dendralenes, including both palladium(II)- and rhodium(I)-catalyzed cycloisomerizations of di-allenes 106 to form cyclic dendralenes 107 (Scheme 1.15) [68, 69, 71], and also the remarkable palladium(0)-catalyzed three-component reaction of di-allenes 108, propargylic carbonates 109, and boronic acids 110 to form bicyclic [3]dendralenes 111 (Scheme 1.15) [70]. Similar, intermolecular transformations to those used to form dendralenes 107 had been reported earlier by Alcaide, to synthesize dihydrofuran-containing dendralenes [72, 73]. 

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