73836-68-7Relevant academic research and scientific papers
Development of an effective chiral auxiliary for hydroxyalkyl radicals
Garner, Philip,Anderson, James T.,Cox, Philip B.,Klippenstein, Stephen J.,Leslie, Ray,Scardovi, Noemi
, p. 6195 - 6209 (2007/10/03)
The development of an effective chiral auxiliary for hydroxyalkyl radicals is delineated. Both the 2-tetrahydropyranyl (THP) and tri-O-benzyl-2-deoxy-α-D-glucopyranosyl (GLU) auxiliaries resulted in diastereoselective radical additions to methyl acrylate at -78°C (ds = 6/1 and 11/1, respectively). The developing stereochemistry at the radical center was completely under auxiliary control. Correlation experiments showed that the D-GLU auxiliary led to attack on the radical Si-face. The selectivity of these radical additions dropped-off considerably when the more reactive 2-nitropropene trap was employed. Computational studies suggested that the observed facial selectivity was due primarily to entropic factors in the transition state but that a smaller temperature-dependent enthalpic contribution was also involved. It was hypothesized that incorporation of a quaternary center at C-6 (THP numbering) would restore the facial selectivity with more reactive radical traps by restricting the orientations available to the incoming alkene. In the event, the trans-6-tert-butyltetrahydropyranyl (tBu-THP) auxiliary resulted in very good diastereoselection with 2-nitropropene (ds = 35/1 at -78°C, 15/1 at 0°C, and 8/1 at RT) as did the tri-O-benzyl-6,6-dimethyl-2-α-D-deoxyglucopyranosyl (diMe-GLU) auxiliary during additions to ethyl α-trifluoroacetoxyacrylate (ds = 10/1 at 0°C). A protocol for recovery of the sugar-derived chiral auxiliaries was also established. This work sets the stage for the development of a novel approach to 1, 3, 5...(2n + 1) polyols based on iterative radical homologation as well as the application of these pyranosidic auxiliaries to other synthetically important reactions.
Stereochemical Studies of the Hydrogenation with an Asymmetrically Modified Raney Nickel Catalyst. The Hydrogenation of Acetylacetone
Tai, Akira,Ito, Kazuhisa,Harada, Tadao
, p. 223 - 227 (2007/10/02)
The hydrogenation of acetylacetone (I) over asymmetrically modified Raney nickel (MRNi) proceeded, step by step, as follows: Step 1 Step 2 acetylacetone (I) ------> 4-hydroxy-2-pentanone (III) ------> 2,4-pentanediol (II).It was demonstrated that the optical yield of Step 1 and the diastereomer excess of Step 2 are governed by the ratio of the stereo-differentiating reaction site to the non-stereo-differentiating reaction site on the catalyst.The stereochemistry of each step was also discussed based on the mode of the intermolecular hydrogen bondings between the substrate and tartaric acid adsorbed on the catalyst.RNi modified with a mixture of tartaric acid and NaBr (TA-NaBr-MRNi) gave the best result with respect to both Step 1 and Step 2.
