Tandem carbonyl coupling-rearrangements promoted by the niobium(III) reagent. Dual reductive and Lewis acid properties of NbCl3(DME)

Geometry determination of tetrasubstituted stilbenes by proton NMR spectroscopy

“…9 Since the reductive elimination is stereospecific, 2,4 we can also conclude that the threo isomer is the diol 2a (δ of the methyl group at 1.54 ppm) and the erythro is 2b (δ of the methyl group at 1.62 ppm). The assignment from recent literature is in this case correct, 5 but older data is contradictory. 10,11 Scheme 4.…”

“…ppm, H arom at 6.9-7.1 ppm). 5 However, simple qualitative inspection of the structures would predict the opposite assignment. Indeed, the aromatic protons in 3a should have usual chemical shifts (around 7.3 ppm), whereas 3b should show a significant shielding, especially for the ortho protons, by the influence of the nearby aromatic ring.…”

Visible light mediated homo- and heterocoupling of benzyl alcohols and benzyl amines on polycrystalline cadmium sulfide

“…Such diols have been obtained in non-photocatalytic conditions by reductive coupling of benzaldehyde or acetophenone using either NbCl 3 (DME) or SmI 2 . 19 para-Methoxybenzyl alcohol-methylether (12) gave in an analogous photoreaction with CdS almost selectively the homocoupling product 13 as a mixture of dl-13 (42%) and meso-13 (47%) as determined by NMR. 20 Ester 14 and p-methoxybenzaldehyde 15 were found in trace amounts of 3 and 4%, respectively, in the product mixture .…”

A Highly Diastereoselective Pinacol Coupling Reaction of Aldehydes and Ketones Using Low-Valence Niobium Generated from Nb(V)

“…This system shows great advantages in that minimize other subsequent reactions of the initially formed pinacols, such as acetal formation and deoxygenation, as observed in Szymoniak's results. 1) To examine this system at a lower temperature, a mixed solvent system was investigated. After optimization, dioxane : toluene (1 : 4) was revealed to be the best solvent and gave 2a with a ratio of 79 : 1 (entry 5).…”