Nickel-Catalyzed Coupling Reaction of 1,3-Disubstituted Secondary Allylic Carbonates and Lithium Aryl- and Alkenylborates
摘要:
This account describes coupling reaction of 1,3-disubstituted secondary allylic carbonates with lithium aryl- and alkenylborates in the presence of a nickel. catalyst. Berates examined are 4, 5, and 6, and reactivity and selectivity were investigated using the allylic carbonates la and Ib. Coupling of la,b with berates 4 was effected with the nickel catalyst, NiCl2(PPh(3))(2) or NiCl2(dppf), in THF at 45-65 degrees C to provide products 3 in good yields with almost 100% regio- and stereoselectivities. Trivalent organoboranes prepared from acetylenes by hydroboration with catecholborane also underwent coupling reaction with la,b after transformation to berates 5 with MeLi. Though coupling using 4 and 5 required elevated temperature (45-65 degrees C), cyclic berates 6 prepared in situ from boronates 8 and MeLi were found to couple with la,b at room temperature or below. Regio- and stereoselectivities were almost 100% as were observed in the cases of 4 and 5. In these reactions, palladium complexes such as Pd(PPh(3))(4), Pd-2(dba)(3) . CHCl3 + 2 PPh(3) showed no catalytic activity. Stereochemical aspect of the present reaction was studied using cyclohexenyl carbonate 24 with 2-furylborate 4e and phenylborate 6a, and was found to proceed with overall anti fashion. With additional experiments, the mechanism of the present reaction was discussed in terms of transient pi-allylnickel intermediates.
Stereoselective synthesis of either (E)- or (Z)-silyl enol ether from the same acyclic α,β-unsaturated ketone using cationic rhodium complex-catalyzed 1,4-hydrosilylation
The stereoselective synthesis of either (E)- or (Z)-silyl enolether from the same acyclic α,β-unsaturated ketone is reported. Highly (Z)-selective conditions were the use of [Rh(cod)2]BF4/DPPE at roomtemperature with no solvent, whereas (E)-selective conditions were the use of [Rh(cod)2]BF4/P(1-Nap)3 (1-Nap = 1-naphthyl) under refluxing dichloromethane.
Tandem Benzylic Oxidation/Dihydroxylation of<i>α</i>-Vinyl- and<i>α</i>-Alkenylbenzyl Alcohols
作者:Rodney A. Fernandes、Pullaiah Kattanguru
DOI:10.1002/hlca.201400143
日期:2015.1
A de novo tandembenzylicoxidativedihydroxylation of α‐vinyl‐ and α‐alkenylbenzyl alcohols has been developed to give α,β‐dihydroxypropiophenones (=2,3‐dihydroxy‐1‐phenylpropan‐1‐ones) and α,β‐dihydroxyalkyl phenones. This method was shown to be substrate‐selective and specific for the oxidation of benzylicalcohols.