The commercially available borane tris(pentafluorophenyl)borane, B(C(6)F(5))(3), is an effective catalyst for the dehydrogenative silation of alcohols using a variety of silanes, R(3)SiH, R(2)SiH(2), and R(2)R'SiH. Generally, the reactions occur in a convenient time frame at room temperature using 2 mol % of the borane and are clean and high yielding, with dihydrogen as the only byproduct. Primary aliphatic alcohols are silated cleanly but slowly, with reaction times ranging from 20 to 144 h. Faster reaction times can be achieved by increasing the catalyst loading to 8 mol % or by heating the reaction to approximately 60 degrees C. Secondary and tertiary alcohols react more rapidly, with most reactions being complete in 0.5-2 h. The reaction is tolerant of many functional groups including C=C, C&tbd1;C, -Br, aliphatic ketones, C(O)OR, lactones, furans, OBn, OMe, and NO(2); examples of each are given. Using the phenolic substrate 2,4,6-trimethylphenol, a number of different silanes were tested. Only the most bulky silanes (Bn(3)SiH and Pr(i)()(3)SiH) were not reactive under these conditions. The selectivity of the silation reactions are roughly governed by the relative basicity of the alcohols (and other functions in the molecule) with more basic groups being selectively silated. These observations are rationalized on the basis of a mechanism that invokes borane activation of the silane by hydride abstraction. The resulting intermediate silylium/hydridoborate ion pair then reacts with alcohols to give the observed silyl ether and dihydrogen products.

Photoinduced asymmetric Wolff rearrangement reactions were performed with alpha-amino-alpha'-methyl-alpha'-diazoketones to afford alpha-methyl-beta-amino acid esters with good stereoselectivity. Factors that may influence the stereochemistry were examined, including steric effects and temperature dependence, which had a great impact on the stereochemistry.

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Trifluoroacetic acid (TFA) was found to promote intramolecular formal N-H insertion reactions. Upon treatment with TFA, optically pure N-Boc-β'-amino-α-diazoketones (5a-c) and N-Boc-γ'-amino-α-diazoketones (10a-d) can be converted, with retention of chirality, into pyrrolidinones (11a-c) and piperidinones (12a-d), respectively, with concomitant removal of the Boc group, in good to excellent yields.Key words: α-diazoketone, amino acid, pyrrolidinone, piperidinone, N-H insertion.

1999 protection, deprotection protection, deprotection O 0345 44 -074 B(C 6 F 5 ) 3 -Catalyzed Silation of Alcohols: A Mild, General Method for Synthesis of Silyl Ethers.-The title borane is an efficient catalyst for the dehydrogenative silation of primary, secondary, and tertiary alcohols. It tolerates a wide variety of functional groups and is effective for a number of different silanes, including some of the more commonly employed silyl ether protecting groups. The reaction times differ greatly, depending on the type of alcohol. In some cases increasing amount of catalyst or heating the reaction make the reactions faster. Compounds with nitrile functions afford long reaction times even under optimization. Phenols with ketone or aldehyde functions in meta-or para-position react with poor chemoselectivity due to competitive reduction of the aldehyde or keto groups. -(BLACKWELL, JAMES M.; FOSTER, KATHERINE L.; BECK, VICTORIA H.; PIERS, WARREN E.; J. Org. Chem. 64 (1999) 13, 4887-4892; Dep. Chem., Univ. Calgary, Calgary, Alberta T2N 1N4, Can.; EN) 1 1999 protection, deprotection 2