A wide-spectrum pulsed magnetic field (WSPMF) was obtained by adjusting the number of current pulses and the pulse interval between adjacent pulses. The effect of WSPMF on the grain refinement of pure aluminium was studied. The distribution of electromagnetic force and flow field in the melt under the WSPMF was simulated to reveal the grain refining mechanism. Results show that the grain refinement is attributed to the combined effect of the melt flow and oscillation under a WSPMF. When the pulse interval is 5 ms, the extreme value of electromagnetic force is the highest, and the size of the crystal nucleus is 0.35 mm. In the case of similar flow rates, the grain size gradually decreases as the pulse interval increases. The range of the harmonic frequency of the magnetic field gradually expands with the increase of the pulse interval, which can provide more energy for nucleation at the solid-liquid interface and promote nucleation.
An enantioselective one‐pot Michael/Michael/Henry/hemiacetalization reaction between α,β‐unsaturated aldehydes, α‐ketoamides, and nitroalkenes under mild conditions catalyzed by a diarylprolinol silyl ether has been developed. The sequential methodology provides a direct approach to a wide range of fully substituted chiral oxabicyclo[2.2.2]octanes with seven contiguous stereocenters in moderate to excellent yields (up to 99%), high to excellent diastereoselectivities (up to >25:1 dr), and high to excellent enantioselectivities (up to 99% ee).
A facile and efficient one‐pot synthesis of isoxazol‐3(2H)‐ones has been developed starting from α‐acyl cinnamides and tosyliminophenyliodinane catalyzed by copper(II) acetate [Cu(OAc)2] under very mild conditions involving a tandem aza‐Michael addition and intramolecular cyclization sequence.