Functional group manipulation via organoselenium- and halogen-induced cyclofunctionalization/hydrolysis of allylic benzimidates, tertiary benzamides, and benzamidines. Regioflexible synthesis of amino alcohol derivatives
摘要:
Allylic benzimidates were treated with benzeneselenenyl halides in chloroform or acetonitrile to give, via 5-exo cyclofunctionalization/hydrolysis, 3-(benzoyloxy)-2-(phenylamino)-1-(phenylselenenyl)-alkanes in fair yields. Allylic tertiary benzamides afforded 2-(benzoyloxy)-3-(phenylamino)-1-(phenylselenenyl)alkanes when submitted to similar reaction conditions. Bromoalkanes, functionalized in an analogous way, were obtained after hydrolytic workup when bromine was added to allylic benzimidates and tertiary benzamides. In some of these reactions, products of 6-endo cyclofunctionalization/hydrolysis (1-(benzoyloxy)-3-(phenylamino)-2-bromoalkanes) were also formed. The addition of benzeneselenenyl bromide to some a-substituted allylic benzimidates and tertiary benzamides was diastereoselective (0 < de < 90%, depending on conditions) with a preference for threo isomer formation. Hydrodeselenation/hydrodebromination of the cyclofunctionalization/hydrolysis products was efficiently effected (88-100% yield) by treatment of the products with triphenyltin hydride in refluxing benzene containing a catalytic amount of azobis(isobutyronitrile). The proper choice of allylic benzimidate/tertiary benzamide allowed the preparation of amino alcohol derivatives in which the 1,2-orientation of the functional groups, relative to the carbon backbone, could be varied in a controlled and predictable manner. The regioflexibility of the process was demonstrated for primary, secondary, and tertiary positions. When allylic benzamidines were submitted to the cyclofunctionalization/hydrolysis reaction conditions using benzeneselenenyl bromide as the electrophilic reagent, 5-phenylselenenyl(methyl) -substituted dihydroimidazoles were obtained.
Increased Efficiency in Cross-Metathesis Reactions of Sterically Hindered Olefins
作者:Ian C. Stewart、Christopher J. Douglas、Robert H. Grubbs
DOI:10.1021/ol702624n
日期:2008.2.1
Efficiency in olefin cross-metathesis reactions is affected upon reducing the steric bulk of N-heterocyclic carbene ligands of ruthenium-based catalysts. For the formation of disubstituted olefins containing one or more allylic substituents, the catalyst bearing N-tolyl groups is more efficient than the corresponding N-mesityl catalyst. In contrast, the formation of trisubstituted olefins is more efficient
Oxazoline-Mediated Interannular Cyclopalladation of Ferrocene: Chiral Palladium(<scp>II</scp>) Catalysts for the Enantioselective Aza-Claisen Rearrangement
作者:Albert Moyano、Malgorzata Rosol、Rosa M. Moreno、Concepción López、Miguel A. Maestro