196951-18-5Relevant articles and documents
Rate dependence on inductive and resonance effects for the organocatalyzed enantioselective conjugate addition of alkenyl and alkynyl boronic acids to β-indolyl enones and β-pyrrolyl enones
Boylan, Amy,Li, Jian-Yuan,Lundy, Brian J.,May, Jeremy A.,Nguyen, Thien S.,Sundstrom, Sasha,Vallakati, Ravikrishna
, (2021/06/16)
Two key factors bear on reaction rates for the conjugate addition of alkenyl boronic acids to heteroaryl-appended enones: the proximity of inductively electron-withdrawing heteroatoms to the site of bond formation and the resonance contribution of available heteroatom lone pairs to stabilize the developing positive charge at the enone β-position. For the former, the closer the heteroatom is to the enone β-carbon, the faster the reaction. For the latter, greater resonance stabilization of the benzylic cationic charge accelerates the reaction. Thus, reaction rates are increased by the closer proximity of inductive electron-withdrawing elements, but if resonance effects are involved, then increased rates are observed with electron-donating ability. Evidence for these trends in isomeric substrates is presented, and the application of these insights has allowed for reaction conditions that provide improved reactivity with previously problematic substrates.
Sequential Two-Step Stereoselective Amination of Allylic Alcohols through the Combination of Laccases and Amine Transaminases
Albarrán-Velo, Jesús,Lavandera, Iván,Gotor-Fernández, Vicente
, p. 200 - 211 (2019/12/03)
A sequential two-step chemoenzymatic methodology for the stereoselective synthesis of (3E)-4-(het)arylbut-3-en-2-amines in a highly selective manner and under mild reaction conditions is described. The approach consists of oxidation of the corresponding racemic alcohol precursors by the use of a catalytic system made up of the laccase from Trametes versicolor and the oxy-radical TEMPO, followed by the asymmetric reductive bio-transamination of the corresponding ketone intermediates. Optimisation of the oxidation reaction, exhaustive amine transaminase screening for the bio-transaminations and the compatibility of the two enzymatic reactions were studied in depth in search of a design of a compatible sequential cascade. This synthetic strategy was successful and the combinations of enzymes displayed a broad substrate scope, with 16 chiral amines being obtained in moderate to good isolated yields (29–75 %) and with excellent enantiomeric excess values (94 to >99 %). Interestingly, both amine enantiomers can be achieved, depending on the selectivity of the amine transaminase employed in the system.
Synthesis of 3-trimethylsiloxy-1-(furan-3-yl)butadiene and its reactions with dienophiles
Mironov, Maxim E.,Bagryanskaya, Irina Yu.,Shults, Elvira E.
, p. 364 - 373 (2021/04/15)
[Figure not available: see fulltext.] 3-Trimethylsilyloxy-1-(furan-3-yl)butadiene was synthesized and studied in reactions with 2,2-dimethyl-5-methylidene-1,3-dioxane-4,6-diones, 5-methylenepyrimidine-2,4,6-triones, as well as with imines. Reactions with dienophiles containing an exo-methylene double bond in the presence of L-proline occurred regio- and stereoselectively with the formation of 7-(furan-3-yl)spiro[5,5]undecane-1,5,9-triones or 7-(furan-3-yl)-2,4-diazaspiro[5.5]undecane-1,3,5,9-tetraones. The reaction of diene with methylene imine, obtained from L-phenylalanine methyl ester and formaldehyde, in the presence of Lewis acids led to the formation of 2-(furan-3-yl)piperidin-4-one or the product of ene reaction, methyl (2S)-2-{[(4E)-5-(furan-3-yl)-3-oxopent-4-en-1-yl]amino}-3-phenylpropanoate. The structures of three compounds were confirmed by X-ray structural analysis.
