We report here an indium(III) triflate (In(OTf) 3 )-catalyzed Prins-type cyclization of disubstituted β-allenols in the presence of aldehydes in dichloromethane (CH 2 Cl 2 ) affording different 3,6-dihydro-2 H -pyran at room temperature or 45 °C. The high efficiency of the reaction and easily available nature of the starting materials/catalyst make it useful in synthesizing different dihydropyran derivatives. A rationale for the formation of all the products was proposed.
2-Alkoxy-3,4-dihydropyrans were proved to be a class of powerful modular substrates to construct polyheterocycles by reacting with NH 2 -containing dinucleophiles, such as anthranilamide , 2-aminobenzenethiol, 1-(2-aminophenyl)pyrrole, and 2-( o -aminophenyl)indole in the presence of LiBr·H 2 O. A three-component reaction of isatoic anhydride , 2-alkoxy-3,4-dihydropyran and amine was also developed as well.
Ling Jiang,Bo Wang,Rong-rong Li,Sa Shen,Hong-wei Yu,Li-dan Ye
Enzymatic catalytic promiscuity has received increasing attention in the past decade. In this research, ten enzymes were investigated for the promiscuous activity in catalysis of the Michael addition-cyclization cascade reaction of p -nitrobenzalacetone with 1,3-cyclohexanedione to prepare 2-hydroxy-2-methyl-4-(4-nitrophenyl)-3,4,7,8-tetrahydro-2 H -chromen-5(6 H )-one in anhydrous media, and control experiments were conducted to exclude false positive results. The highest yield (46.1%) was observed with Escherichia coli BioH esterase and the optimal reaction condition was: 1 mmol α,β-unsaturated ketone, 1 mmol 1,3-dicarbonyl compound, 20 mg E. coli BioH esterase, 20 ml N,N-dimethylformamide at 37 °C for 120 h. To preliminarily investigate the mechanism, site-directed mutagenesis was performed on the hydrolysis catalytic triad of BioH, and the results indicated “alternate-site enzyme promiscuity”. When a series of substituted benzalacetones and 1,3-cyclic diketones were used as the reactants, yields of up to 76.3% were achieved. These results imply the potential industrial application of E. coli BioH in the preparation of dihydropyran derivatives.
The reductive amination (RA) of 2-hydroxytetrahydropyran (2-HTHP) produced from biofurfural-derived dihydropyran provides a new efficient process for the clean synthesis of valuable 5-amino-1-pentanol (5-AP). Among various solid catalysts tested, the inexpensive Ni–Mg3AlOx catalysts derived from hydrotalcite precursors were found to be very active and selective, especially at Ni loadings above 20 wt %. A 85% total yield of 5-AP was obtained from dihydropyran on 40Ni–Mg3AlOx, the catalyst with the highest 2-HTHP RA activity among the Ni–Mg3AlOx catalysts, under mild conditions of 60 °C and 2 MPa H2. Characterization results showed that the reducibility of the calcined NiO-Mg3AlOx samples increased with increasing Ni loading from 5 to 50 wt %, while the Ni0 crystallite sizes exhibited a minimum of 4.8 nm on 40Ni–Mg3AlOx after reduction in H2 at 750 °C. The volcanic changes of 5-AP generation rate/yield with increasing Ni loading of the Ni–Mg3AlOx catalysts and with rising prereduction temperature of 30Ni–Mg3AlOx catalyst in 2-HTHP RA indicate that the balance of the reducibility and Ni0 particle size of the catalysts played an important role in obtaining high 5-AP yields. The 30Ni–Mg3AlOx catalyst showed a good stability in 2-HTHP RA examined in a continuous flow reactor over a 90 h time-on stream.
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