10.1002/anie.201109072
The study presents the development of a microporous binol-derived phosphoric acid catalyst for asymmetric organocatalysis. The researchers synthesized a new chiral 1,1’-binaphthalene-2,2’-diol (binol)-derived phosphoric acid (BNPPA) and used it to create a microporous polymer network. This network, which contains the molecular catalyst, ensures high density and accessibility of catalytic centers, leading to fast reaction rates. The BNPPA was used in various asymmetric reactions, including transfer hydrogenation of prochiral benzoxazines, asymmetric Friedel–Crafts alkylation of pyrroles, and aza-ene-type reactions. The microporous polymer network demonstrated high enantioselectivity and activity comparable to its homogeneous counterpart, with the added benefits of being reusable and easily separable. The study highlights the potential of this new heterogeneous catalyst for various asymmetric synthetic transformations.
10.1246/cl.1987.355
The study presents a convenient method for preparing optically active 1,1'-binaphthyl-2,2'-diol via enzymatic hydrolysis of its racemic diester using commercially available porcine pancreatic lipase (PPL). The researchers found that PPL could efficiently and enantioselectively hydrolyze the valeric acid diester of racemic 1,1'-binaphthyl-2,2'-diol, yielding the (S)-diol with 95% enantiomeric excess (ee) at a 46% conversion rate. The reaction was conducted by stirring an emulsion of the diester in a mixture of ethanol, hexane, and phosphate buffer with PPL. The study highlights the potential of this method as an alternative to the conventional, more tedious optical resolution process, and mentions ongoing efforts to scale up the process and develop a method for reusing the lipase.
10.1016/j.jorganchem.2009.09.037
The research focuses on the development of an efficient synthetic method for the preparation of chiral α-methylene-γ-butyrolactones, which are important building blocks for the creation of biologically active compounds. The study utilizes the indium-catalyzed enantioselective allylation of aldehydes with β-carbonyl allylstannanes, yielding optically active homoallylic alcohols that can be further converted to the corresponding optically active α-methylene-γ-butyrolactones. The researchers found that the reactions between N-aryl β-amido allyltributylstannanes and aromatic aldehydes were particularly effective, providing high enantioselectivity. They demonstrated the catalytic enantioselective allylation using 10 mol% of In(S,S)-iPr-pybox3 or 15 mol% of [In(S)-BINOL]Cl3 complexes. Key chemicals used in the process include various aldehydes, β-carbonyl allyltributylstannanes, chiral indium complexes as catalysts, and chiral ligands such as (S)-4-isopropyl-2,6-bis(oxazolin-2-yl)pyridine and BINOL. The study concludes that the developed methods not only offer catalytic and enantioselective allylation but also enable the synthesis of optically active α-methylene-γ-butyrolactones without the need for chiral allyltributylstannanes prepared through laborious procedures.
10.1055/s-1997-982
The study investigates the catalytic asymmetric reduction of various ketones using transient hypervalent silicon hydrides derived from trialkoxysilanes. The trialkoxysilanes, upon activation by a small amount of a chiral nucleophile, react with the carbonyl group of ketones to form silyl-protected alcohols, which are then cleaved to yield enantiomerically enriched alcohols. The researchers conducted a screening of reaction parameters and found that the use of certain chiral catalysts, such as the monolithio salts of (R)-binol and its derivatives, in combination with solvents like ether and additives like TMEDA, significantly enhanced both the yield and enantioselectivity of the reductions. The study demonstrated that steric effects around the carbonyl group of the ketones played a crucial role in determining the enantioselectivity of the products.
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