Versatility of organoborane

The versatility of organoboranes was explored during the early years of hydroboration chemistry. Conversions to several classes of functional groups, such as alcohols, amines, ketones, alkenes, acetylenes, dienes, enynes, etc. were achieved with ease. 

In conclusion, we have reviewed the utility of the products from allylboration of aldehydes with B-allyldiisopinocampheylborane for the synthesis of lactones of varying ring sizes. This is yet another example of the versatility of organoboranes in asymmetric syntheses. 

The ready availability of organoboranes next prompted a detailed exploration of their reactions, with emphasis on reactions of utility in synthesis. This exploration proved to be remarkably fruitful—it is clear that the organoboranes are the most versatile organometallic available to the chemist (47, 48). 

The versatility of the organoboranes as synthetic precursors provided the basis for subsequent studies centered on the incorporation of stable and radioisotopes of elements other than hydrogen. 

Olefin metathesis of vinylboronates [102] and allylboronates [103, 104] has been investigated over the past few years because organoboranes are versatile intermediates for organic synthesis. Cross metathesis of vinylboronate 108 and 2-butene 109, for example, yields the boronate 110, which can be converted to the corresponding vinyl bromide 111 with high Z selectivity. Vinyl iodides can be obtained analogously. It should be noted that vinyl bromides and vinyl... 

Hydroboration made the organoboranes readily available for the first time. This led to a systematic exploration of the chemistry of the organoboranes and established the fact that they constitute the most versatile organometallic available presently. A major new area awaits exploration and application. 

ORGANOBORANE. A compound composed of an unsaturated organic group and a borane obtained by the hydroboration reaction. Such compounds are useful catalytic reagents in organic syntheses of some complexity, e,g, cis- or (/awf-olefins, optically pure alcohols, alkanes, and ketones. Prostaglandins and insect pheromones have been synthesized by tlus means. A particularly versatile example is triphenylboron B(CgHsty. See also Borane Carborane and Hydroboration. 

H. C. Brown, Organoborane-Carbon Monoxide Reactions. A New Versatile Approach to the Synthesis of Carbon Structures, Accounts of Chemical Research 2, 65 (1969). 

The method is particularly attractive since the first stage, known as hydroboration, can be applied to almost any nonaromatic carbon-carbon multiple bond and exhibits very useful selectivity features. Hydroboration is also the most attractive means of synthesizing organoboranes, which are arguably the most versatile organometallic reagents available to the organic chemist. The reaction has received extensive... 

Hydroboration of cw-alkenes with these reagents creates new chiral centers. Oxidation of the resultant organoboranes with retention furnishes alcohols of predictable absolute stereochemistry. IPC2BH is perhaps one of the most versatile chiral reagents for laboratory use. A rationalization of the observed stereoselectivities has been proposed. Under similar experimental conditions but using (-t-)-Ipc2BH, hydroboration of cw-2-butene produces the (-h)-(5) alcohol. 

Another method for preparing functional Ziegler-Natta polymers is to use an organoborane mediated synthesis. This method has been extensively studied and reviewed by Chung . The success of this technique results from these factors (a) trialkyl boranes are Lewis acids, which are stable to Z-N catalysts, (b) they are soluble in Z-N (hydrocarbon) solvents, (c) they are remarkably versatile synthons for a variety of functional groups. In this case, borane functional alpha olefin monomers (31) are polymerized to polyboranes which can be hydrolyzed to a variety of functional groups. 

These versatile reactions, commonly referred to as Stille and Suzuki couplings, respectively, are performed with organostannanes or organoboranes as nucleophiles and are tolerant to most functional groups. Ketones are obtained if carbon monoxide is present in the Stille reaction. This gives the possibility to label an aromatic methyl ketone in two different positions by the use of either [ C] carbon monoxide or [ C] methyl iodide, as shown in O Fig. 41.22 (Andersson et al. 1995 Andersson and Langstrom 1995a, b). 

The Suzuki reaction is palladium-catalyzed coupling of organic halides or tri-flates with organoboranes under basic conditions. The organic halides and tri-flates react in the order of 1 > Br > OTf Cl. The reaction provides a highly versatile procedure for the construction of new carbon-carbon bond that tolerates many functional groups [1]. 

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