Catalytic asymmetric synthesis of polysubstituted cyclohexa-1,3-dienes from ?-branched ?,?-alkenals

Amine‐Promoted Asymmetric (4+2) Annulations for the Enantioselective Synthesis of Tetrahydropyridines: A Traceless and Recoverable Auxiliary Strategy

“…[1] One of the most versatile and reliable methods to prepare this class of six-membered heterocycles is the aza-Diels-Alder reaction. [2] Particularly, the recent development of dienamine catalysis [3] has added a powerful dimension to the aza-Diels-Alder reaction, which strongly relies on the formation of the dienamines developed by the groups of Barbas, [4] Jørgensen, [5] and Chen [5] by 1,2-addition of the amine catalyst to enone or enal (Scheme 1). Despite extensive studies and noteworthy…”

Amine‐Promoted Asymmetric (4+2) Annulations for the Enantioselective Synthesis of Tetrahydropyridines: A Traceless and Recoverable Auxiliary Strategy

“…[2] Particularly, the recent development of dienamine catalysis [3] has added a powerful dimension to the aza-Diels-Alder reaction, which strongly relies on the formation of the dienamines developed by the groups of Barbas, [4] Jørgensen, [5] and Chen [5] by 1,2-addition of the amine catalyst to enone or enal (Scheme 1). Despite extensive studies and noteworthy advances in this field, the utilization of 2-methylene-3-oxobutanoate, a molecule potentially prone to polymerization, [6] as an enone-type substrate remains challenging.…”

The effect of pressure on the diastereoselectivity of the reaction of prenal with monoalkyl ylidenemalonates catalysed by homochiral secondary amines

“…Recently, the catalytic synthesis of optically active cyclohexa-1,3-dienes from β-branched α,β-alkenals and various monoalkyl ylidenemalonates was described, 1 and factors affecting the apparent (net) enantioselectivity of this process were studied. 2 The reaction mechanism (Scheme 1) 1-3 involves the transient formation of a dienamine followed by two consecutive, inherently diastereoselective reactions.…”

“…Since the net enantioselectivity of cyclohexadiene formation diminishes with temperature, 1,2 we used a high-pressure technique as an alternative to heating for accelerating the process without damaging the ee of its products. Scheme 2 demonstrates two examples examined.…”

“…At both pressures, the work-up of the reaction mixture included its concentration in vacuo, the extraction of an oily residue with pentane, and the fractionation of the pentane-extracted solute by column chromatography (SiO 2 ). The purity of the products was controlled by TLC on Silufol plates (hexane-AcOEt, 6:1; R f 0.55 for 3 and 0.45 for 5) and by 1 H NMR spectroscopy (Bruker AM-300 instrument, in d 6 -benzene). Enantiomer ratios (er) and the values of ee in scalemic 3 and 5 were determined by correlating the [a] D of a specimen with the ratio of peak areas belonging to R and S antipodes in the 1 H NMR spectrum recorded in the presence of (S)-or (R)-BINOL (for details, see refs.…”