Michael addition boron trifluoride etherate

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. ... 

A recent total synthesis of tubulysin U and V makes use of a one-pot, three-component reaction to form 2-acyloxymethylthiazoles <06AG(E)7235>. Treatment of isonitrile 25, Boc-protected Z-homovaline aldehyde 26, and thioacetic acid with boron trifluoride etherate gives a 3 1 mixture of two diastereomers 30. The reaction pathway involves transacylation of the initial adduct 27 to give thioamide 28. This amide is in equilibrium with its mercaptoimine tautomer 29, which undergoes intramolecular Michael addition followed by elimination of dimethylamine to afford thiazole 30. The major diastereomer serves as an intermediate in the synthesis of tubulysin U and V. 

The reaction of 3-(3,4-dimethoxyphenyl)propanoic acid with thallium(III) trifluoroace-tate in the presence of boron trifluoride etherate leads to a mixture of the dihydrocoumarin (574) and the spirolactone (572) (78JOC3632). It is suggested that these products arise through an initial one-electron oxidation to the radical cation, the fate of which may vary. Thus, intramolecular reaction with the carboxyl group gives the radical (571) and eventually the spirolactone. Alternatively, capture of the radical ion by solvent and further oxidation affords the radical (573), whereupon an intramolecular Michael addition to the carboxyl group and aromatization lead to the dihydrocoumarin (Scheme 218) (81JA6856). 

Conjugate additions of dialkylcuprates to (3-substituted-a,P-unsaturated acids and esters give low yields. Addition of boron trifluoride etherate, BFj-OEtj, to certain dialkylcuprates and higher-order cuprates enhances their reactivity in Michael additions to conjugated acids and esters. 

Velezheva and coworkers described the Lewis acid-catalyzed Nenitzescu indolization using zinc iodide in dichloromethane (Scheme 9, equation 1 and 43-45) [23], later improved to the use of zinc chloride (equations 2, 3) [24]. Boruah and colleagues employed a Lewis acid-catalyzed microwave-modified Nenitzescu indolization to prepare 3-amino-5-hydroxybenzo[ ]indoles (Scheme 9, equation 4, and 46-47) [25]. Boron trifluoride etherate was superior to other Lewis adds studied (TiCl, AICI3, ZnClj, InCy. The reaction presumably proceeds by a Michael addition of the carbonyl component, in the form of a p-hydroxyenamine to the naphthoquinone, and the urea serves as a controlled-release source of ammonia. 

Dealkylation of Ethers. The combination of an aliphatic thiol such as ethanethiol and boron trifluoride etherate has been used to remove benzyl groups. However, although that method works well it does suffer from an incompatibility with certain functional groups. The presence of an a,/3-unsaturated ester in the same molecule can result in Michael addition as well as debenzylation (eq 1). Boron trifluoride in the presence of dimethyl sulfide, being a milder reagent, does not cause this type of complication, as shown in eq 2. ... 

Reported examples of the second reaction occur at the j8-position in an a,a -disubstituted pyrrole. Whilst for the second reaction there is no evidence to indicate the intermediate formation of ethyl methylenemalonate, followed by Michael addition, pyrroles can participate in such additions. Examples are the ready reaction with ethynyl ketones , with quinones" and with acrylic esters (in the presence of boron trifluoride etherate)" ... 

Substituted 4,5-dihydro-6H-l,3-thiazines (27) are formed in high yields by Michael addition of thioamides, thioureas, or thiocarbamates (25) to the double bond of a 3-unsaturated aldehydes, ketones, or ketols (24) in the presence of boron trifluoride etherate and subsequent spontaneous ring-closure of the resulting intermediate (26). In some instances the products (27) can be converted into the corresponding 6H-l,3-thiazines, c.g. (28), with POCI3 in pyridine or with acid in aprotic solvents. 

Complexes, such as 1, also readily react with anions of amines the effect of added Lewis acids was investigated boron trifluoride-diethyl ether complex exerted little effect upon the reaction, but addition of titanium(IV) chloride or tin(lV) chloride inhibited the Michael addition45. 

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