Synthetic Applicability and in Situ Recycling of a B-Methoxy Oxazaborolidine Catalyst Derived from cis-1-Amino-indan-2-ol

Abstract

A procedure is described that greatly simplifies the use of an oxazaborolidine catalyst derived from (1R,2S) cis-1-amino-indan-2-ol. This B-OMe catalyst has been employed in the asymmetric reduction of a number of structurally diverse prochiral ketones, in particular the reduction of alpha-amino acetophenone and its derivatives. A method for reducing the effective catalyst loading by "in situ recycling" is also presented. [structure: see text]

The use of marine-derived fungi for preparation of enantiomerically pure alcohols

“…Since the corresponding racemic reduction product (±)-β-phenylalcohols 2a-2m (except 2b) were not commercially available, they were obtained by reduction of the aromatic ketones 1a and 1c-1m with sodium borohydride in methanol (Pavia et al 1999) and used as standard compounds for analysis of bioreduction products via chiral HPLC. The NMR spectra of synthesized standard racemic compounds 2a and 2c-2m are shown in the Supporting Information and are in agreement with those reported in the literature (Gilmore et al 2004;Inagaki et al 2010;Matharu et al 2005;Olivares-Romero and Juaristi 2008).…”

“…Final chemical yields of more than 92% was achieved and the product ee was maintained above 99%. The absolute configurations of the reduction products (S)-2a, (S)-2b, (R)-2c, (S)-2d, (S)-2g, (S)-2h, (S)-2i, (S)-2j, and (R)-2l obtained by enzymatic reduction were determined by comparing the specific signs of rotation measured for the isolated products to those reported in the literature (Gilmore et al 2004;Inagaki et al 2010;Matharu et al 2005;Olivares-Romero and Juaristi 2008), except for (S)-2b, for which the absolute configuration was determined by co-injection of commercially available (R)-2b onto chiral HPLC.…”

“…The spectroscopic data ( 1 H and 13 C NMR, and HPLC retention times) of enantiomeric alcohols 2a-2d, 2g-2j, and 2l are in agreement with those obtained for racemic forms, as described above. The optical rotations of isolated enantiomeric alcohols 2a and 2c, 2d, 2g-2j, and 2l are as follows: (S)-2a, [α] D 2 0 -38.5 (c 1.00 in MeOH), lit [Gilmore et al 2004] [Gilmore et al 2004] [α] D 20 -30.9 (c 1.00 in CHCl 3 ) for (R)-2c; (S)-2d, [α] D 20 + 9.68 (c 0. 05 in MeOH), lit [Gilmore et al 2004] [Du et al 2006]…”

Catalytic enantioselective addition of methyltriisopropoxititanium to aldehydes

“…(R)-3,3-Dimethylbutan-2-ol (2o): 24 Following the general procedure A, the reaction of pivaldehyde (11.0 µL, 0.1 mmol) with methyltriisopropoxytitanium (0.20 mL, 2.0 equiv., 1.0 M in THF) in the presence of (Ra,S)-Ph-BINMOL L1 (3.8 mg, 0.1 equiv.) in Et2O (1.5 mL) provided (R)-3,3-dimethylbutan-2-ol.…”

Preparation and Characterization of Chiral Oxazaborolidine Complex Immobilized SBA‐15 and Its Application in the Asymmetric Reduction of Prochiral Ketones

“…The enantioselectivity of borane reduction may be affected by reaction conditions such as solvent and reaction temperature. [24,25] As it has been reported that THF is the better solvent than toluene and dichlorome- thane, [26] THF was used as the solvent in this study. As can be seen in Table 2, the reaction temperature (À78 8C, 0 8C, room temperature, refluxing conditions) has a profound effect on the enantioselectivity of the product.…”