Phenylboronates, hydrolysis

An interesting asymmetric transformation is the asymmetric conjugate addition to a-acetamidoacryhc ester 30 giving phenylalanine derivative 31, which has been reported by Reetz (Scheme 3.10) [10]. The addition of phenylboronic acid 2m in the presence of a rhodium complex of l,T-binaphthol-based diphosphinite ligand 32 gave a quantitative yield of 31 with up to 11% enantiomeric excess. In this asymmetric reaction the stereochemical outcome is determined at the hydrolysis step of an oxa-7r-aUylrhodium intermediate, not at the insertion step (compare Scheme 3.7). 

You can prepare phenols in large quantities by the pyrolysis of the sodium salt of benzene sulfonic acid, by the Dow process, and by the air oxidation of cumene. Each of these processes is described below. You can also prepare small amounts of phenol by the peroxide oxidation of phenylboronic acid and the hydrolysis of diazonium salts. 

Efficient asymmetric 1,4-addition of phenylboronic acid to cyclohexenone, followed by hydrolysis, affords 3-phenylcyclohexanone (473) with 97% ee using Rh-BINAP as a catalyst [183a]. 

The B-G bond of allyl-, alkynyl-, aryl-, and benzylboranes is more easily cleaved than that of alkylboranes. The C-B bond of aromatic boronic acids is stable to water, but polyfluorinated phenylboronic acids are exceptionally sensitive to Me0H-H20-K0H and Me0H-H20-pyridine.488 Allylic organoboranes were hydrolyzed with water at room temperature with complete allylic rearrangement (Equation (102)).489,490 Addition of water resulted in the rapid hydrolysis of benzylic G-B bond of 329 due to the electron-withdrawing effect of Cr(CO)3 group (Equation (103)).491... 

The hydrolysis of salicylaldehyde imines is catalyzed by boric acid, substituted arylboronic acids, and diphenylborinic acid. The effects of different substituted phenyl-boronic acids on the rate of hydrolysis at pH 6.0 has been studied by Rao and Philipp [168]. The second-order rate constants, are higher for phenylboronic... 

Pentanediol [(R,/ )-28] has been used for the formation of chiral acetals and as a precursor for chiral alkenes (Sections D.1.5.1. and 1.6.1.5.). The original procedure for the resolution of the phenylboronic acid derivative with brucine39 was impractical, but recently a kinetic resolution by lipase-catalyzed esterification and hydrolysis has been developed40. In addition, a good method for catalytic reduction of 1,3-diketones with Raney nickel modified with sodium bromide and tartaric acid (for a procedure, see Section D.2,3.1.) allowed the production for commercial purposes41. Similarly, sterically more hindered and less water-soluble 2,6-dimethyl-3,5-heptanediol (29) has been introduced for the same purpose. It is obtained in the same way from the diketone and separated from the meio-compound by simple recrystallization42. 

The catalysts are thought to be hydroxorhodium species (45), formed upon hydrolysis of the rhodium precursor. Part of the mechanism for the addition of phenylboronic acid to 37 is shown in Scheme 8.20. 

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