1,3,2-Benzodioxaboroles

Several oxygen- and sulfur-substituted boranes have been reported (125—130). 1,3,2-Benzodioxaborole [274-07-7] (catecholborane, CB) (15) is the one best studied. It is commercially available or can be prepared by the reaction of catechol with borane-THF (57,131), or by other procedures (132). The product is a Hquid existing as a monomer, remarkably stable to disproportionation. No... 

Hydroboration, the addition of a boron-hydrogen bond across an unsaturated moiety, was first discovered by H. C. Brown in 1956. Usually, the reaction does not require a catalyst, and the borane reagent, most commonly diborane (B2H6) or a borane adduct (BH3-THF), reacts rapidly at room temperature to afford, after oxidation, the /AMarkovnikov alkene hydration product. However, when the boron of the hydroborating agent is bonded to heteroatoms which lower the electron deficiency, as is the case in catecholborane (1,3,2-benzodioxaborole) 1 (Scheme 1), elevated temperatures are needed for hydroboration to occur.4 5... 

Scheme 40. 1,3,2-Dioxa- (78) and 1,3,2-Benzodioxaboroles (79), Analogues of Purines (80), and Pentaphenylborole (82)...

Catecholborane (1,3,2-benzodioxaborole) with a purity of 95% was purchased from Aldrich Chemical Company, Inc. and purified by distillation under nitrogen, bp 58°C (52 mm). For the distillation and handling of air and moisture sensitive compounds, see references 3-5. Catecholborane is a liquid at room temperature, and the neat material is 9.0 H in catecholborane. The preparation of catecholborane from borane and catechol has been reported. ... 

The reaction of potassium dienoxy borates with A-fluorobis(phenylsulfonyl)amine (la) gives y-fluoro enones in good yield. The potassium dienoxy borates are prepared by treating potassium enolates derived from unsaturated ketones with 2-phenyl-1,3,2-benzodioxaborole. This methodology offers a convenient alternative to the traditional fluorination of dienol acetates, ethers, or enamines.145 An example is given by the formation of 13.145... 

Benzodioxaboroles (79) are easily hydrolyzed by water at room temperature. Attention has been paid to the parent 1,3,2-benzodioxaborole (79 R = H) as a hydroborat-ing agent of alkenes and alkynes to give, after hydrolysis, alkyl- and alkenyl-boronic acids. Compound (79 R = H) is oxidized by dry air at room temperature (75JA5249). 

In the hydroboration/oxidation reaction of 2-cyclohexen-l-ol derivatives the regio- as well as the stereoselectivities can be steered in either of two directions by use of different reagents and reaction conditions. Dialkylboranes, e.g., 9-BBN, give mainly tn rs-l,2-diols, whereas with 1,3,2-benzodioxaborole ( catecholborane") in the presence of the rhodium hydrogenation catalyst Rh(PPh3)jCl the trans-1,3-diols become predominant. The cis- 1,2-diols are usually only formed in trace amounts, but the cis-l,3-diols are always produced as byproducts in 10 — 20% yield (D.A. Evans, 1988). 

Alkyl-l,3-dienes. Palladium black, prepared from Pd(OAc)2 and B2H6, is the most effective catalyst for head-to-tail cross-coupling of 1-alkenyl iodides with 1-alkenyl-1,3,2-benzodioxaboroles to give mainly 2-alkyl-1,3-dienes (equation I).1... 

Stereospecific synthesis of (2Z,4E,6E)-3,7,11-trimethyl-2,4,6,10-dodecatetraene, trans (Cio)-allofamesene 49), isolated from Perilla fmtscem Makino, was realized by the ptdladium-catalyzed cross-coupling of 4,8-dimethyl-l,3,7-nonatrienyl-l,3,2-benzodioxaborole 48) with (Z)-2-bromo-2-butene. The benzodioxaborole derivative 48) was prepared by hydroboration of 4,8-dimethylnona-3,7-dien-l-yne 47), obtained via two steps from geranial, with 1,3,2-benzodioxaborole (Eq- 112) Bombykol and its geometrical isomers were also synthesized selectively... 

Table 3. Selected Chiral Alcohols via Catalytic Asymmetric Hydroboration/Oxidation of Alkenes with 1,3,2-Benzodioxaborole...

Acyclic dialkoxyboranes, (RO)2BH, readily disproportionate, 4 but a number of heterocyclic analogs, such as the trimethyldioxaborinane (1), catecholborane (2 1,3,2-benzodioxaborole) and 1,3,2-dithiaboro-... 

---