Boron esters

A number of boron chemicals are prepared directly from boric acid. These include synthetic inorganic borate salts, boron phosphate, fluoborates, boron ttihaHdes, borate esters, boron carbide, and metal aHoys such as ferroboron [11108-67-1]. 

Table 3. Synthesis of ort/io-Substituted Fluoroaromatics from Nitrite Esters, Boron Trifluoride, and Hydrogen Fluoride [26]...

The sources of the required organoboron compounds are manifold. The most popular organoboron compounds for this method, boronic acids and their esters (boronates), can be obtained through ... 

Savarin, C. Srogl, J. Liebeskind, L. S. Thiol ester-boronic acid cross-coupling. Catalysis using alkylative activation of the Pd thiolate intermediate. Org. Lett. 2000, 2, 3229-3231. 

Perfluoroalkyllithium reagents react with electrophiles such as aldehydes, ketones, silicon and tin halides, alkyl halides, carbonates, esters, boron trifluoride-imine complexes, and sulfur dioxide. ... 

This section covers the formation of cyclopropanes via cyclization of reactive allylic intermediates (cations, anions, radicals). Included are those transformations of allylic functional derivatives (e.g. allylic halides, alcohols, aldehydes, ketones, acids, esters, boronates, Grignard reagents) to cyclopropyl derivatives that do not actually proceed via allylic reactive intermediates, but which are not covered by other sections of this volume. Additionally, this section will cover methods for the formation of cyclopropanes by pericyclic reactions. 

Medium and large rings can be made via cationic intermediates which are usually generated by treatment of suitable precursors with acid. Reactions of this class are perchloric acid catalyzed rearrangements of bicyclo[n.l.0]alkan-2-ols (n > 5), solvolysis of the corresponding esters, boron trifluoride-diethyl ether complex catalyzed cleavage of epoxides, and tri-fluoroacetic acid catalyzed reactions of 7-(methylsulfanyl)bicyclo[n.l.0]alkanes. 

Hydroboration of alkenes and alkynes is an established preparative method of alkyl- and alkenylboranes. Arylboranes, arylboronic acids and their esters (boronates) are prepared from aryllithium or Grignard reagents. 

CAS 688-74-4 EINECS/ELINCS 211-706-5 Synonyms Borane, tributoxy- Borester Boric acid, tributyl ester Boron tributoxide Butyl borate... 

Synonyms Boric acid, triisopropyl ester Boric acid, tris (1-methylethyl) ester Boron isopropoxide Boron triisopropoxide Isopropyl borate... 

Synonyms Boric acid, trimethyl ester Boron methoxide Methyl borate Trimethoxyborane Trimethoxyborine Trimethoxyboron... 

Carbonyl substituents on boronic esters normally require two intervening carbons between the carbonyl group and the boronic ester boron. It is not entirely clear why direct acylborane (0=C-B) linkages are unstable. The enol ether of an acetylboronic ester, pinanediol (l-methoxyvinyl)boronate, has been synthesized [39], but it proved too sensitive to allow chloromethyl insertion into the C-B bond [39], and attempts to hydrolyze it to the acetylboronic ester were unproductive. 

The simplest way to think about the pK, of boronic acids is to consider a solvent water molecule associated with the sp boronic acid, at high pH the water is deproto-nated and forms a tetrahedral sp boronate. On saccharide binding and formation of a cyclic boronate ester the pJC of the boronic acid is lowered, or in other words the ester is more acidic than the acid . The enhanced acidity is due to a bond angle compression on formation of a cyclic boronate ester. Boronic acids have a 120 (sp ) bond angle but on the formation of a cyclic ester the bond angle is reduced to 108 . Obvi-... 

The detection of boron by this color reaction is adversely affected by oxidizing agents and fluorides. The former give a red or yellow color with the reagent fluorides form fluoboric acid or boron fluorides and so prevent the production of the colored ester. Boron can be detected in the presence of these materials under certain conditions, but the sensitivity is then lower. 

The primary interaction of a boronic acid with a diol is covalent and involves the rapid and reversible formation of a cyclic boronate ester. Boronic adds are therefore ideally suited to the recognition of saccharides in water, overcoming the problem of solvation inherent in synthetic receptors reliant on hydrogen-bonding interactions. 

---