Chiral crystallization of optically inactive (achiral) compounds such as benzophenone, phenol, phenanthrene, etc. has not been a commonly known phenomenon in organic chemistry. These compounds are known to crystallize to chiral crystals from their solutions. This review deals with this phenomenon, describing (1) what is chiral crystallization and how to find organic compounds undergoing chiral crystallization, (2) the preparation of chiral crystals from achiral organic compounds, (3) the characterization of chiral crystals, (4) the crystal structure of chiral crystals and the factors of the generation of chirality, (5) the chiral crystallization of two-component molecular compounds, (6) absolute asymmetric synthesis utilizing chiral crystallization, (7) other applications of chiral crystallization. Part 2 describes chapters (5), (6), and (7).
The first total synthesis of the microbial a-pyrone meroterpenoid, (+) -pyripyropene A (1), acyl-CoA : cholesterol acyltransferase (ACAT) inhibitor, which is effective and concise convergent approach (14 steps, 9.3% overall yield), designed to afford easy access to both the natural products and a variety of analogs, has been achieved. The key step is the coupling reaction between a-pyronepyridine moiety (4) and the acid chloride of sesquiterpene moiety (3) in the presence of Lewis acid to construct ketone (2). The sesquiterpene moiety has been synthesized started from (+) -Wieland-Miescher ketons via stereoselective reductive formylation, palladium associated carbonylation, and allylic oxidation. (+) -Pyripyropene E (36) also has been synthesized from farnesyl acetate (9 steps, 9.6% overall yield). The convergent and stereoselective route exploited a biomimetic polyene cyclization as the key transformation.
In this article, chemo-enzymatic syntheses of important substances which serve as the building blocks for glycoconjugate synthesis are described : 1) Sialic acid aldolae-catalyzed synthesis of sialic acids and its analogs ; 2) Studies on Rhodococcus rhodochrous IFO 15564-catalyzed degradation of N-acetyl-D-glucosamine and its derivatives ; 3) Hydration of carbohydrate nitriles mediated by a nitrile hydratase produced by R. rhodochrous IFO 15564 ; 4) Synthesis of N-acetyl-D-allosamine based on the lipase-catalyzed regioselective acetylation as the key step ; 5) Kinetic optical resolution of highly deoxygenated carbohydrate by means of lipase-catalyzed transesterification ; 6) Kinetic optical resolution of ceramide based on lipase-catalyzed hydrolysis.
Reported herein are the developments and applications of new silole-containing σ- and π-electronic systems. A series of 2, 5- and 1, 1-difunctionalized. siloles have been prepared based on the intramolecular reductive cyclization of diethynylsilanes. Starting from these functionalized siloles, oligo (2, 5-silole) s and oligo (1, 1-silole) s have been synthesized as model compounds for poly (2, 5-silole) s and poly (1, 1-silole) s, respectively, which are still veiled target molecules in this field. Some silolebased π-conjugated cooligomers and copolymers with thiophene, pyrrole, and acetylene π-electronic systems have been prepared and their photophysical properties have been determined. Application of silole π-electronic systems to organic electroluminescent (EL) devices has also been examined.
This review deals with new optically active phosphine ligands which appeared in the literature during past eight years. Emphasis is laid on the utility of these ligands in transition metal-catalyzed asymmetric reactions. New methods for the synthesis of chiral phosphine ligands are also described.
The Wittig reaction and its variants produce no sp3 stereocenter, nevertheless asymmetric transformation from achiral carbonyl compounds can be achieved by using optically active phosphorus reagents. These approaches are based on three different methodologies, kinetic resolution and discrimination of either π-face of carbonyl or enantiotopic carbonyl groups in the symmetrical molecules. A variety of phosphorus reagents has been reported and used for these transformations. Among the Horner-Wadsworth-Emmons (HWE) type reagents, those possessing 8-phenylmenthyl or binaphthyl groups as a chiral auxiliary exert high level of asymmetric induction. For example, the HWE reagent of binaphthyl group effectively discriminated the carbonyl face giving dissymmetric olefins, and differentiated enantiotopic carbonyls of meso-α-diketones to afford the Z- and E-olefins with high optical yield. This discrimination was successfully applied to the practical one-pot procedure for optically active allenic compounds as well as the construction of the fused ring systems through the intramolecular HWE reaction.