Boron compounds propargylic compound reactions

To elucidate the reaction pathway, deuterium-labeled allenyl pinacol boronate 10 was prepared, and the addition reaction with hydrazonoester 6 was conducted in the presence of Bi(OH)3 and Cu(OH)2 (Scheme 4). In both Bi- and Cu-catalyzed cases, the reactions proceeded smoothly (in quantitative yields in both cases). In the Bi(OH)3-catalyzed reaction, a major product was allenyl compound 11, in which the internal position was deuterized. It was assumed that a propargyl bismuth was formed via transmetalation from boron to bismuth, followed by addition to hydrazonoester via y-addition to afford allenyl compound 11. Thus, two y-additions could selectively provide a-addition products [75, 76, 105, 106]. It was confirmed that isomerization of 10 did not occur. Recently, we reported Ag20-catalyzed anti-selective a-addition of a-substituted allyltributyltin with aldehydes in aqueous media [107], On the other hand, in the Cu(OH)2-catalyzed reaction, a major product was propargyl compound 12, in which the terminal position was deuterized. A possible mechanism is that Cu(OH)2 worked as a Lewis acid catalyst to activate hydrazonoester 6 and that allenyl boronate 10 [83-85] reacted with activated 6 via y-addition to afford 12. 

Extension of this reaction to electrophiles other than aldehydes was unsuccessful [22, 23], However, propargylic boronates were found to react with allylic halides and various carbonyl compounds [23], The boronates were prepared by lithiation of a methyl-substituted alkyne with t-butyllithium followed by treatment with a trialkylborane. The propargylic boronate preferentially reacts with the electrophile at the y-position to yield propargylic products (Eq. 9.20). The methodology has also been applied to alanates with comparable results. 

Carbonyl Allylation and Propargylation. Boron complex (8), derived from the bis(tosylamide) compound (3), transmeta-lates allylstannanes to form allylboranes (eq 12). The allylboranes can be combined without isolation with aldehydes at —78°C to afford homoallylic alcohols with high enantioselectivity (eq 13). On the basis of a single reported example, reagent control might be expected to overcome substrate control in additions to aldehydes containing an adjacent asymmetric center. The sulfonamide can be recovered by precipitation with diethyl ether during aqueous workup. Ease of preparation and recovery of the chiral controller makes this method one of the more useful available for allylation reactions. 

The reactions of allenyl and propargyl derivatives of boron, silicon or tin with carbonyl compounds or acetals take place with double-bond migration (Se reactions). Therefore, allenyl derivatives will lead to homopropargyl alcohols and propargyl analogs to allenyl alcohols. 

MERCURIO (Italian, Spanish) (7439-97-6) Violent reaction with alkali metals, aluminum, acetylenic compounds, azides, boron phosphodiiodide (vapor explodes), bromine, 3-bromopropyne, chlorine, chlorine dioxide, ethylene oxide, lithium, metals, methyl silane (when shaken in air), nitromethane, peroxyformic acid, potassium, propargyl bromide, rubidium, sodium, sodium carbide. Forms sensitive explosive products with acetylene, ammonia (anhydrous), chlorine, picric acid. Increases the explosive sensitivity of methyl azide. Mixtures with hot sulfuric acid can be explosive. Incompatible with calcium, sodium acetylide, nitric acid. Reacts with copper, silver, and many other metals (except iron), forming amalgams. 

The reaction of propargyl alcohols with dicobalt octacarbonyl to give the complex salts 148 (X = BF4 or PF6) and synthetic uses of the latter have been reviewed. The salts react with electron-rich aromatic compounds ArH, such as anisole, phenol or N,N-dimethylaniline, to yield substitution products 149 after oxidative demetallation with an iron(III) or cerium(I V) salt with j5-diketones or j -keto esters the corresponding propargyl-substituted compounds 150 are obtained k Acetone reacts in an analogous fashion to give 151. The action of the cobalt complexes 148 on allylsilanes 152 leads to enynes 153. Indole reacts with the complex 148 (R = H R = R = Me) in the presence of boron trifluoride etherate to give 154, which was converted into 155 by the action of iron(III) nitrate " ... 

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