Fa-Guang Zhang

Chiral bifunctional thiourea-catalyzed enantioselective Michael addition of ketones to nitrodienes.

Simple bifunctional thioureas, derived from the commercially available saccharides and chiral diamines, have been shown tunably to promote Michael-type addition of ketones to alpha,beta-gamma,delta-nitrodienes. The Michael adducts were obtained in good yields albeit with high enantioselectivites (84-99% ee). Furthermore, these products can be readily transformed into more useful molecules.

Enantioselective Base‐Free Electrophilic Amination of Benzofuran‐2(3H)‐ones: Catalysis by Binol‐Derived P‐Spiro Quaternary Phosphonium Salts

However, enantioselective synthesis of such significant chiral benzofuran-2(3H)-ones remains a considerable challenge. Catalytic enantioselective introduction of substituents at the C3 position represents the most direct approach to chiral benzofuranones. For instance, Vedejs et al. and Hill and Fu have presented the asymmetric Black rearrangement of Oacylated benzofuranones by means of chiral derivatives of 4dimethylaminopyridine (DMAP) to afford enantioenriched C-acylated isomers with up to 98 % enantiomeric excess. Very recently, two other groups reported the enantioselective conjugate addition reactions of benzofuran-2(3H)-ones to a,b-unsaturated carbonyl compounds, in which chiral thioureas and amines were used as catalysts. Enantioselective introduction of a heteroatom group at the C3 position would substantially broaden the benzofuranone chemistry and offer more functionalized chiral products. Herein, we present a hitherto unknown catalytic enantioselective amination of benzofuranones by employing a new class of rigid chiral Pspiro quaternary phosphonium salts as organocatalysts. Over the past decades, organocatalysis that exploits the use of chiral quaternary ammonium salts has emerged as an area of intense interest in asymmetric synthesis owing to its operational simplicity and mild reaction conditions. 8] A number of quaternary ammonium salt catalysts have demonstrated useful levels of enantioselectivity in a wide range of asymmetric reactions. Furthermore, a recent breakthrough in this field involved the design and application of chiral quaternary phosphonium salts in catalytic asymmetric synthesis. For examples, the group of Ooi developed a series of P-spiro tetraaminophosphonium salts as chiral Brønsted acids for substrate recognition and functional-group activation through hydrogen bonding. Maruoka and co-workers reported other chiral quaternary tetraalkylphosphonium salts and their use in asymmetric phase-transfer catalysis. Despite the above mentioned progress, this field is still in its infancy and the construction of new phosphonium catalysts is still in great demand to meet the need of many challenging asymmetric reactions. Since 1,1’-binaphthyl-based enantiopure chiral materials are among the most readily available privileged sources of chirality, chemical modification of binaphthyls resulting in the formation of new modular structures for catalytic application has been a proven strategy for the development of novel chiral catalysts. We envisioned that the introduction of two chiral 2,2’-bis(methylene)-1,1’-binaphthyl moieties onto a phosphorus center would form a rigid P-spiro tetraalkylphosphonium framework, thus enabling a high level of asymmetric induction. A series of novel homochiral tetraalkylphosphonium bromides 1 possessing a [7.7] spirocyclic core were readily prepared by the reaction of (S)-4,5-dihydro-3Hdinaphtho[2,1-c :1’,2’-e]phosphepine with (S)-3,3’-disubstituted 2,2’-bis(bromomethyl)-1,1’-binaphthyls and purified in analytically pure form after one simple recrystallization. Crystals suitable for X-ray diffraction analysis were obtained for the quaternary phosphonium salt 1a. The ORTEP view of this structure is shown in Figure 2. As expected, the two binaphthylmethylene units are twisted at the phosphorus center. The dihedral angle between the planes of the two naphthyl units is 69.18. It was expected that the conformational rigidity imposed by the P-spiro scaffold could potenFigure 1. Examples of chiral benzofuran-2(3H)-ones.

Regioselective Cycloaddition of Trifluorodiazoethane with Electron-Deficient Allenic Esters and Ketones: Access to CF3-Substituted Pyrazolines and Pyrazoles

A highly regioselective cycloaddition procedure of electron-deficient allenes with trifluorodiazoethane (CF3CHN2) is described. In absence of bases, the reaction proceeded smoothly to give 5-(trifluoromethyl)pyrazolines, whereas the utility of Et3N led to the formation of 3-(trifluoromethyl)pyrazoles.

Photoelectric automatic focusing system based on interference

The principle and the method of a new automatic focusing system are presented in this paper. The system is constructed relying on the relationship between laser wave interference patterns and defocusing displacement. A CCD linear array receives interference patterns in the form of light intensity, which are converted into digital signals afterwards. Then the computer controls a stepping motor to complete auto-focusing process according to the digital results. The system has been applied in a kind of film resolution testing instrument and it shows that it has the advantage of high accuracy, high speed and wide applications.

One-Pot Cascade Transformations of Zinc Trifluorodiazoethylide and α,β-Unsaturated Enones: Access to Trifluoromethylated Polycyclic Pyrazolines

One-pot cascade transformations are developed that involve [3 + 2] cycloaddition/Michael/aldol and [3 + 2] cycloaddition/double 1,2-addition reactions of zinc trifluorodiazoethylide with various α,β-unsaturated enones. The protocol provides straightforward access to trifluoromethyl-substituted polycyclic pyrazolines with high chemo-, regio-, and diastereoselectivity.

Direct Regioselective [3 + 2] Cycloaddition Reactions of Masked Difluorodiazoethane with Electron-Deficient Alkynes and Alkenes: Synthesis of Difluoromethyl-Substituted Pyrazoles

Phenylsulfone difluorodiazoethane (PhSO2CF2CHN2), an easy-to-prepare and bench-stable masked CF2-building block, has been developed. The synthetic utility of this reagent is demonstrated by a direct regioselective [3 + 2] cycloaddition with electron-deficient alkynes and alkenes. This protocol enables facile construction of an array of difluoromethyl-substituted pyrazoles in good to high yields under mild reaction conditions.

Telescoping Reactions with Trifluorodiazoethane-Derived Aza-Wittig Reagents and Allenyl esters

A telescoping process involving the consecutive addition of four reagents (trifluorodiazoethane, phosphine, allenyl ester, and acetic acid) into a single reactor was developed for the novel functionalization of allenyl esters. First, new phosphazenes derived from trifluorodiazoethane and phosphines were generated and reacted with allenyl esters to give unexpected α-iminophosphoranes through the creation of C=P, C=N, and C-H bonds at the α-, β-, and γ-carbon atoms, respectively, of the allenyl esters. The α-iminophosphoranes did not react with aldehydes in a classic Wittig reaction, but instead β-enamino esters were obtained. The overall sequence of reactions offered a formal hydrohydrazonation of allenyl esters. The method was extended to other related diazo compounds and applied to the preparation of novel 5-pyrazolone derivatives. Not only is the telescoping process described herein an effective approach for truncating the multistep synthesis, but also each step has been dissected to understand and support the reaction mechanisms.