[reaction: see text] Asymmetric Michael additions of cyclohexanone to both aryl and alkyl nitroolefins in the presence of 20 mol % of organocatalyst 2b and 10 mol % of n-butyric acid afford adducts 5 with high diastereoselectivities and enantioselectivities.

[Reaction: see text]. Ylides are nucleophiles that bear a unique leaving group, L n M, and can attack aldehydes, ketones, imines, and electron-deficient alkenes. Over the course of the reaction, they react with CX (X = C, N, O, etc.) double bonds to form betaine or oxetane intermediates, which further eliminate the heteroatom-containing group in one of two ways to give the corresponding olefination or cyclization product. Since the discovery of the Wittig reaction, ylide olefination has developed as one of the most useful approaches in constructing carbon-carbon double bonds. These reactions provide unambiguous positioning of the C-C double bond and good stereoselectivity. Researchers have also widely used ylides for the synthesis of small ring compounds such as epoxides, cyclopropanes, and aziridines. However, the use of ylides to prepare larger cyclic structures was very limited. This Account outlines our recent work on ylide-initiated Michael addition/cyclization reactions. By altering the heteroatoms and the ligands of the ylides, we have modulated the reactivity of ylides. These modified ylides provide easy access to diverse cyclic compounds with the ability to control regioselectivity, chemoselectivity, diastereoselectivity, and enantioselectivity. Reactions using these ylides produce the structural components of many biologically active compounds and valuable intermediates in organic synthesis. Allylic telluronium and sulfonium ylides can react with alpha,beta-unsaturated esters, ketones, amides, and nitriles to afford multisubstituted vinylcyclopropanes with high selectivities. Telluronium allylides react with aromatic N-phenyl aldimines to give trans-vinylaziridines and with chiral N- tert-butylsulfinylimines to afford the optically active cis-2-substituted vinylaziridines, both with high diastereoselectivities. We also used sulfonium and telluronium allylides to prepare vinylepoxides. In addition, ylides are good reagents for the synthesis of five-membered heterocyclic compounds. By treatment of stable camphor-derived sulfur ylides with alpha-ylidene-beta-diketones, we obtained multisubstituted dihydrofurans with high diastereo- and enantioselectivities. Ammonium salts derived from cinchonidine and cinchonine react smoothly with 3-aryl and 3-heteroaryl-2-nitro acrylates, affording both enantiomers of isoxazoline N-oxides with up to 99% ee. Ylides can initiate tandem cyclizations for the synthesis of chromenes, bicyclic compounds, and cyclohexadiene epoxides. Varying the choice of base allows access to 2 H-chromenes and 4 H-chromenes from 3-(2-(bromomethyl)phenoxy)acrylates via a tandem ylide Michael addition/elimination/substitution reaction. Phosphines can catalyze an intramolecular ylide [3 + 2] annulation constructing bicyclo[ n.3.0] ring systems with three contiguous stereogenic centers. The reaction of crotonate-derived sulfur ylides with alpha,beta-unsaturated ketones affords cyclohexadiene epoxides with excellent diastereoselectivities (>99/1) in good to high yields. Using a camphor-derived sulfo...

In asymmetric catalysis, the remote control of enantioselection is usually difficult due to the long distance communication between the chiral center of the catalyst and the reactive site of the substrate. The development of efficient and highly enantioselective catalysts for such reactions is of great importance and highly desirable. The stereocontrol over an asymmetric reaction is a delicate process (ca. 3.0 kcal/mol difference in transition states can lead to >99/1 enantiomeric selectivity at room temperature), it therefore requires fine-tuning on the electronic nature of the central metal together with a precisely created cavity to accommodate the substrates and reagents. We envision that a solution is the design of new catalysts by finding an easy and efficient way to tune the electronic properties, the chiral space, and the shape of the catalytic site. Since an extra coordination group in the organometallic complex could not only alter the microenvironment around the metal center in a three-dimensional manner but also tune the electronic properties of the metal center, about 10 years ago, we introduced a side arm strategy for ligand/catalyst design. This Account describes our efforts toward this goal. Based on this side arm strategy, we have developed two series of ligands based on the bisoxazoline framework; namely, trisoxazoline (TOX) ligands and side armed bisoxazoline (SaBOX). The "side arms" are shown to play multiple roles in different cases, for example, as a ligating group, a steric group, or a directing group, which are dependent on the metal and the functionality at the side arm. Metal catalysts based on these ligands have proven to be highly efficient for a number of asymmetric transformations, including Friedel-Crafts reaction, Kinugasa reaction, Nazarov reaction, 1,2-Stevens rearrangement, Cannizzaro reaction, and cyclopropanation. In comparison with the parent BOX ligands, the metal catalysts based on these TOX and SaBOX ligands usually exhibit higher efficiency and diastereo- and enantioselectivity with better impurity tolerance and stability. Moreover, in several TOX-metal complex catalyzed reactions such as Friedel-Crafts reaction and [3 + 2] cycloaddition, stereoselectivity could be switched based on reaction conditions. These ligands were particularly prominent in the remote controls of enantioselection such as the conjugate additions to alkylidene malonates and ring-opening/cyclization cascades of cyclopropanes, for which high stereoselectivity is usually difficult to achieve due to the poor chiral communication. The works by us and other groups have demonstrated that the side arm strategy can be employed as a general principle for ligand and catalyst design and should not be limited to the BOX scaffolds and the reactions described in this Account. Wide application of the new strategy in organometallic homogeneous catalysis can be anticipated.

All zipped up: Titanium complexes are designed as efficient catalysts for the copolymerization of ethylene with polar olefins, such as ω‐alkenol and ω‐alkenoic acid. An organophosphine catalyst can be zippered on the polyethylene (see scheme; TBS=tert‐butyldimethylsilyl, FG=functional group, MMAO=modified methylaluminoxane) to form an efficient and recoverable initiator for [3+2] cycloaddition.

Diamond, a crystalline form of carbon, shows exceptional physical and chemical properties, such as the highest known hardness and elastic modulus. These characteristics have been attributed to its specific 3D atomic packing and strong sp 3 tetrahedral covalent bonds. [1,2] Attempts to design analogous materials, including molecular sieves and metal-organic frameworks (MOFs), [3,4] have centered on ensuring the same packing as that of diamond, which has 3D facecentered-cubic Fd3 m symmetry.Ordered mesoporous materials have received enormous attention owing to their high surface areas, regular frameworks, and large pore sizes with narrow distribution, all of which lead to multiple potential applications. [5,6] Ordered mesoporous carbon, which is one of the most promising materials, possesses both remarkable functional properties and excellent chemical/thermal stability, which makes it suitable for applications in catalysis, [7] sensing, [8] bioreactor construction, [9] and energy storage. [10] Recently, a family of highly ordered mesoporous carbon with p6mm, Im3 m, and Ia3 d symmetries has been synthesized by an organic-organic self-assembly strategy with PEO-PPO-PEO triblock copolymers as templates (PPO: polypropyleneoxide; PEO: polyethyleneoxide). [11][12][13][14][15] Among the various mesostructures, 3D cubic mesopore geometries are attractive owing to their promise, especially in host-guest chemistry. [16,17] However, the synthesis of mesoporous materials with a 3D cubic Fd3 m structure, which is a unique structure with a bimodal pore size distribution, has not been reported to date by using triblock copolymers as templates. This attractive mesostructure with a silicate composition has only been obtained thus far by using laboratory-made tri-head-group cationic (for FDU-2) [18] and anionic (for AMS-8) surfactants as templates [19,20] under very strict synthetic conditions. In addition, the mesoporous silicas obtained have small lattice parameters and their bimodal mesopore systems cannot be detected by N 2 sorption measurements owing to the smaller size of the surfactant molecules compared to block copolymers.Amphiphilic PEO-PPO-PEO triblock copolymers, which are commercially available as Pluronics or Synperonics, have been proven to be versatile and efficient templates for the fabrication of ordered mesoporous silicas with different symmetries.[21] PPO-PEO-PPO triblock copolymers are another family of commercial surfactants that have the hydrophilic PEO block located in the middle and the hydrophobic PPO blocks at either end of the polymer chain. They are rarely used in the synthesis of ordered mesoporous silicas, however, because of the difficulty of forming oil-inwater micelles. [22][23][24] Reverse PPO-PEO-PPO copolymers with long PEO segments can reduce the curving energy and result in micellar interconnected networks, [24] the possible fascinating phase behaviors of which may provide them with good structure-directing properties for the fabrication of facecentered-cubic Fd3 m mesostructures with high curv...

A series of novel titanium(IV) complexes bearing monoanionic [O-NX] (X = O, S, Se) ligands is designed by sidearm approach. These complexes were synthesized, characterized, and employed as catalysts in ethylene homo- and copolymerization. X-ray diffraction studies on these new compounds reveal a distorted octahedral coordination of the central metal with the three chlorine ligands in a mer disposition. In the presence of modified methylaluminoxane (MMAO), they exhibit moderate to high activity and afford highly linear polyethylene. Variation of the sidearm, including different heteroatom and substituents, proves to modulate both the catalytic activity and the molecular weight of the resulting polyethylene. The complexes also show excellent capability in copolymerization of ethylene with 1-hexene.

Novel titanium complexes containing monoanionic [NOP] ligands based on a phenoxyimine ligand and their derivatives were synthesized and characterized. Their performance as ethylene polymerization and copolymerization catalysts were studied. Upon treatment with MMAO, the [NOP]TiCl 3 complexes were robust and highly active for the polymerization of ethylene, even at very low cocatalyst/catalyst ratios. These catalysts also have good copolymerization capabilities.

An enantioselective formal [3+3] annulation reaction of cyclic ketones with enones has been developed. In the presence of 20 mol % of pyrrolidine-thiourea 1a or N-(pyrrolidin-2-ylmethyl)trifluoromethanesulfonamide 1i, the reactions afford bicyclo [3.3.1] adducts in moderate to good yields with good to high enantioselectivities under mild conditions.