The asymmetric organocatalyzed diversity-oriented one-pot synthesis has been developed to construct chroman-2-one derivatives and other heterocyclic compounds with excellent efficiency and stereoselectivity. The reactions represent a challenging issue, since it altered the inherent selectivity profiles exhibited by the substrates of 2-hydroxycinnamaldehyde 1 and trans-β-nitrostyrene 2, which was previously reported as the asymmetric oxa-Michael-Michael cascade to generate chiral chromans. It should be noted that polycyclic O,O-acetal-containing compounds, which are found in numerous natural products and biologically interesting molecules, could also be achieved in good yields with excellent enantioselectivity as a single diastereoisomer with five continuous stereogenic centers.
Based on the appropriate choice of electrophiles, one-pot, multicomponent, enantioselective domino reactions have been realized which contain a five-step sequence and provide highly efficient access to potentially bioactive chroman-2-one derivatives as a single diastereoisomer with excellent enantioselectivities and in high yields. This new strategy could significantly improve the previous protocol by directly starting from commercial 2-hydroxybenzaldehydes rather than preformed lactols, which have to be synthesized in several additional steps.
Titanium tetrachloride can be reduced by lanthanum filings to the corresponding low valent titanium complex, which can induce some aromatic aldehydes to the corresponding pinacols in 28%-97% yields within 10-50 min in ethyl acetate at r.t. under ultrasound irradiation.
Polyphenylalkane derivatives Q 0720Pinacol Coupling of Aromatic Aldehydes and Ketones Mediated by TiCl4-Zn in Ethyl Acetate under Ultrasound. -The title procedure is characterized by mild reaction conditions, short reaction times and involvement of an environmentally benign solvent. The dl/meso ratio of the resulting pinacol is influenced by the aryl substituents.-(LI*, J.-T.; SUN, X.-L.; LIN, Z.-P.; CHEN, Y.-X.; LI, T.-S.; Indian J. Chem., Sect.
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