Ruthenium(II)-Catalyzed Asymmetric Transfer Hydrogenation of Ketones Using a Formic Acid−Triethylamine Mixture

Chemical Synthesis of the GHIJK Ring System and Further Experimental Support for the Originally Assigned Structure of Maitotoxin

“…Scheme 2 depicts the enantioselective construction of the G-ring intermediate 13 from prochiral furan derivative 3 and features a Noyori reduction with catalyst 6 [8] as a means to introduce chirality into the emerging molecule. Thus, lithiation (nBuLi) of furan 3 [9] in THF at 0 8C followed by the addition of Weinreb amide 4 [10] at À78 8C afforded ketone 5 (91 % yield), which was then reduced asymmetrically with the (S,S)-Noyori catalyst 6 (5 mol %) in a 5:2 mixture of formic acid/triethylamine at 25 8C (94 % yield, > 95 % ee) to afford, after selective pivaloate protection of the primary hydroxy group (PivCl, 2,6-lut., 92 % yield), chiral furan 7.…”

Chemistry of the Synthetic Strigolactone Mimic GR24

“…Therefore, we elected to modify a procedure described by Cignarella and co-workers [18] to generate the indanone 12, which could subsequently undergo the stereo-defining Noyori asymmetric transfer hydrogenation. [19] As shown in Scheme 2, 3-benzoylpropionic acid (13) was subjected to an aldol reaction with formaldehyde followed by in situ lactonisation to give compound 14. [18] Careful control of pH was critical for achieving a satisfactory yield for this transformation as excessive acid favoured a competing elimination reaction.…”

Preparation and Catalytic Performances of a Molecularly Imprinted Ru‐Complex Catalyst with an NH2 Binding Site on a SiO2 Surface

“…Homogeneous Ru-TsDPEN derivatives have proved to be highly efficient for asymmetric transfer hydrogenation. [91][92][93] A carbamate group (-NHCOO-) connected to a silane coupling moiety (-SiA C H T U N G T R E N N U N G (OC 2 H 5 ) 3 ) was tethered to the alcohol template, and cleavage of the carbamate moiety after appending the silane coupling branch on the wall of a molecularly imprinted cavity produced a spatially arranged NH 2 binding site for the hydrogenation of o-fluorobenzophenone. An advanced catalytic system combining an active Ru complex, a shapeselective reaction space with a similar shape to the template, and a spatially arranged molecular binding site for o-fluorobenzophenone hydrogenation was successfully prepared on the surface of SiO 2 .…”

“…[98] It is well known that derivatives of Ru-TsDPEN complexes are also highly efficient for asymmetric transfer hydrogenation. [91][92][93] Indeed, the homogeneous Ru complex (B) converted 98 equivalents of o-fluorobenzophenone (o-F-BP) in 1 day, as shown in Table 1. The supported Ru complex (D), with a similar local coordination to B, exhibited similar enantioselectivity in the asymmetric transfer hydrogenation of o-F-BP (55 % enantiomeric excess (ee) (S)) and o-methylbenzophenone (o-Me-BP) (71 % ee (S)).…”