Tri boron

Arylboronic acids are readily available via transmetalation between ArSnMe3 and borane in THF. Consequently, a variety of arylpolyboronic acids is achievable from the stannanes previously synthesized by the SRN1 mechanism from ArCl or ArOH in around 80% yields [50, 51]. These arene di- and tri-boronic acids can be used as starting materials for the synthesis of polycyclic aromatic systems via double or triple Suzuki crosscoupling reactions [50, 51], as shown in Scheme 10.34 [51],... 

The ring systems now known to form such stacked organometallic arrays include mono- and di- as well as tri-boronated derivatives of the cyclopentadienyl anion (BR)x(C R )5 similar derivatives of benzene (IiR)i((T ),j,ijL... 

R. Benesch May I ask one last question, and that is, what special electrodes were you thinking of Corwin tried boron and carbon electrodes, and he didn t find any reversibility there, either. 

Platinum(0)-catalyzed diboration of 1-alkynylboronates with bis(pinacolato)dibo-rane yielded the corresponding trisboronated alkene products in high yields (Scheme 9.58) [120]. Catalyzed diboration of styrylboronate esters in the presence of either [Rh(PPhj)3Cl] or [Rh(COE)2(li-Cl)]2 and two equivalents of P(o-tol)j yielded predominantly the corresponding alkenyl tris(boronate) [121]. 

Fig 28, Comparison of tri-boron alkylborazole retention times on Carbowax 4000 and on squalane,... 

Boron tri-iodide, Blj (BClj plus HI at red heat or I2 plus NaBH ), m.p. 43°C, b.p. 2iO°C. It has very similar properties to boron trichloride. 

Other boron hydrides are known, most of them having the general formula B H + 4- for example pentaborane, B5H9, decaborane, BjqHi4. Each can be made by heating diborane in suitable conditions for example at 420 K, decaborane is obtained. Boron hydrides have been tried as rocket fuels. 

Sihcon and boron bum ia fluorine forming siUcon tetrafluoride [7783-61-17, SiF, and boron trifluoride [7637-07-2] respectively. Selenium and tellurium form hexafluorides, whereas phosphoms forms tri- or pentafluorides. Fluorine reacts with the other halogens to form eight interhalogen compounds (see Fluorine compounds, inorganic-halogens). 

In addition, boron, aluminum, and gallium tris(triduoromethanesulfonates) (tridates), M(OTf)2 and related perduoroalkanesulfonates were found effective for Friedel-Crafts alkylations under mild conditions (200). These Lewis acids behave as pseudo haUdes. Boron tris(tridate) shows the highest catalytic activity among these catalysts. A systematic study of these catalysts in the alkylation of aromatics such as benzene and toluene has been reported (201). 

The reaction of 2-methyla2iridine with boron trichloride [10294-34-5] lea.ds to replacement of all three chlorides by ayiridine rings to form tri(methylethyleneimine) boron [17862-61-2] (152). The reaction of boron trifluoride [7637-07-2] with ethyleneimine at — 78°C proceeds via substitution and subsequent ring opening to yield A/-P-fluoroethyl-fl-difluorobora2ene (153). 

A noteworthy development is the use of KH for complexing alkylboranes and alkoxyboranes to form various boron hydrides used as reducing agents in the pharmaceutical industry. Potassium tri-j -butylborohydride [54575-50-7] KB(CH(CH2)C2H )2H, and potassium trisiamylborohydride [67966-25-0] KB(CH(CH2)CH(CH2)2)3H, are usefiil for the stereoselective reduction of ketones (66) and for the conjugate reduction and alkylation of a,P-unsaturated ketones (67). 

The tri-, tetra-, penta-, and hexahydrates of boron phosphate have been reported. AH of these decompose rapidly in water to give solutions of the parent acids. Anhydrous boron phosphate hydroly2es in a similar fashion, though the reaction proceeds quite slowly for material that has been ignited at high temperatures. 

Synthesis. One of the more common routes for the synthesis of aminoboranes involves the aminolysis of the appropriate boron hahde. Trisaminoboranes are most convenientiy prepared by adding BCI3 to an excess of amine in an inert solvent at low temperatures (42). For example for tris(dimetby1amino)borane [4375-83-1]. ... 

Many polymers containing boron in the main chain have been prepared but most of them have either been of low molecular weight or intractable cross-linked structures. Some interest has been shown in the tri-3-aminoborazoles, which polymerise on heating (Figure 29.15f. ... 

If ethoxyacetylene is allowed to react in an anhydrous system with aliphatic ketones in the presence of boron trifluoride etherate, the unsaturated acid is obtained directly. This variation apparently has not yet been tried on steroids. 

Alkyl silyl ethers are cleaved by a variety of reagents Whether the silicon-oxygen or the carbon-oxygen bond is cleaved depends on the nature of the reagent used Treatment of alkoxysilanes with electrophilic reagents like antimony tri-fluonde, 40% hydrofluonc acid, or a boron tnfluonde-ether complex results in the cleavage of the silicon-oxygen bond to form mono-, di-, and tnfluorosiloxanes or silanes [19, 20, 21) (equations 18-20)... 

Molybdenum hexafluoride, in the presence of boron trifluonde, reacts with acetic acid and haloacetic acids at 130-160 °C to give respectively, 1,1,1 tri fluoroethane and 1,1 1 trifluorohaloetlianes in 60-89% yields [2d0, 241] Prolonged treatment of pyridine mono and dicarboxylic acids with an excess of molybdenum hexafluoride at elevated temperatures provides the respective mono-and bis(trifluoromethyl)pyridines in good yields [241] (equation 127)... 

Perfluoroallyl fluorosulfate is prepared by the treatment oiperfluoropropene with sulfur tnoxide m the presence of boron catalysts [2, 3, 4, 5, 6, 7] (equation 2) Perfluoroisopropyl allyl ether reacts similarly to give 58% polyfluoroallyl fluorosulfate in a cis/trans ratio of 6 4 [S] Sultones are the exclusive products without catalyst. Polyfluoroolefins such as 2-hydropentafluoropropylene [9], (2,3-dichloropropyl)tri-fluoroethylene [70], perfluoropropene [2, i], perfluoroisopropyl alkenyl ethers [S], and acyclic polyfluoroallyl ethers [77] undergo sulfur trioxidation to regioselectively produce the corresponding P-sultones in high yield... 

Thermal cleavage of boron tris(trifluoromethane)sulfonate and boron tris(pen-tafluoroethane)sulfonate was studied. Careful identificadon of the products has led to the proposal of a mechanism and an account for this process [121] (equation 93). 

Boron trifluoride etherate, is also a good catalyst for this hydride transfer to chalcone. Unlike triphenylmethyl perchlorate, however, chalcone is able to enter Michael additions with the 1,5-diketone followed by eliminations leading to unexpected products, e.g., 3-benzyl-2,4,6-triphenylpyrylium from 2-carbethoxy-l,3,5-tri-phenylpentane-l,5-dione and chalcone the benzyl group originates from chalcone, the elimination product being ethyl benzoylacetate. ... 

In the next step, one of the borane-hydrogens is transferred to a sp -carbon center of the alkene and a carbon-boron bond is formed, via a four-membered cyclic transition state 6. A mono-alkyIborane R-BH2 molecule thus formed can react the same way with two other alkene molecules, to yield a trialkylborane R3B. In case of tri- and tctra-substituted alkenes—e.g. 2-methylbut-2-ene 7 and 2,3-dimethylbut-2-ene 9—which lead to sterically demanding alkyl-substituents at the boron center, borane will react with only two or even only one equivalent of alkene, to yield a alkylborane or mono alky Iborane respectively ... 

Now we can expect that boron will be tri-valent. We predict that there should be molecules such as BH3 and BF3... 

Scheme 5 details the asymmetric synthesis of dimethylhydrazone 14. The synthesis of this fragment commences with an Evans asymmetric aldol condensation between the boron enolate derived from 21 and trans-2-pentenal (20). Syn aldol adduct 29 is obtained in diastereomerically pure form through a process which defines both the relative and absolute stereochemistry of the newly generated stereogenic centers at carbons 29 and 30 (92 % yield). After reductive removal of the chiral auxiliary, selective silylation of the primary alcohol furnishes 30 in 71 % overall yield. The method employed to achieve the reduction of the C-28 carbonyl is interesting and worthy of comment. The reaction between tri-n-butylbor-... 

Treatment of commercially available and symmetrical 3,4,5-tri-methoxytoluene (37) with iodine, periodic acid, and acetic acid under the conditions of Suzuki19 results in the formation of symmetrical diiodide 38 in 93 % yield. Although only one of these newly introduced iodine atoms is present in intermediate 13, both play an important role in this synthesis. Selective monodemethylation of 38 with boron trichloride furnishes phenol 39 in 53% yield together with 13 % of a regioisomer. Evidently, one of the Lewis-basic iodine substituents coordinates with the Lewis-acidic boron trichloride and directs the cleavage of the adjacent methyl ether... 

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