The first example of Fe-catalyzed enantioselective azidations of β-keto esters and oxindoles using a readily available N3-transfer reagent is reported. A number of α-azido-β-keto esters were obtained with up to 93% ee, and this methodology also generates 3-substitued 3-azidooxindoles with high enantioselectivities (up to 94%).

A new class of chiral tridentate N-donor pincer ligands, bis(oxazolinylmethylidene)isoindolines (boxmi), was synthesized in three steps starting from readily available phthalimides. Their reaction with ethyl (triphenylphosphoranylidene)acetate by means of a key-step Wittig reaction gave the ligand backbones, which were condensed with amino alcohols and then cyclized to obtain the corresponding ligands. These ligands were subsequently applied in the nickel(II)-catalyzed enantioselective fluorination of oxindoles and β-ketoesters to obtain the corresponding products with enantioselectivities of up to >99% ee and high yields. Application of the chiral pincer ligands in the chromium-catalyzed enantioselective Nozaki-Hiyama-Kishi reaction of aldehydes gave the corresponding alcohols with an optimal enantioselectivity of 93%.

Enantioselective Cu-catalyzed trifluoromethylation of β-ketoesters using commercially available trifluoromethylating reagents is reported. A number of α-CF(3) β-ketoesters are obtained with up to 99% ee. The trifluoromethylated products were then transformed diastereoselectively to α-CF(3) β-hydroxyesters with two adjacent quaternary stereocenters via a Grignard reaction.

Direct functionalization of CÀH bonds is an appealing strategy in organic synthesis [1] but its practical application has so far been difficult to realize. The selective functionalization of primary C À H bonds of alkanes that also contain secondary and/or tertiary C À H bonds is a great challenge, as CÀH bond energy follows an order primary > secondary > tertiary. [1c,d] In seminal works by Bergman, [1b] Jones, [1c] and their respective co-workers, stoichiometric reactions of alkanes with [Cp*(Me 3 P)M] (Cp* = C 5 Me 5 ; M = Rh, Ir) resulted in the formation of C À M bonds by selective activation of primary C À H bonds. Subsequent work by Hartwig and coworkers [1g,i, 2] demonstrated C À B bond formation by stoichiometric and catalytic functionalization of primary CÀH bonds mediated by tungsten, rhodium, or ruthenium complexes. The high selectivity for primary CÀH bond functionalization in these C À M or C À B bond-formation reactions (Scheme S1 in the Supporting Information) is considered to result from kinetic factors or steric interaction between the metal complexes and alkanes. [1i, 3] A well-established process in CÀC bond formation by direct CÀH bond functionalization is the metal-catalyzed intra-and intermolecular carbenoid insertion into C À H bonds, with diazo compounds as the carbene source. [1o, 4] These catalytic C À C bond-formation reactions generally feature lower selectivity for primary CÀH bonds than for secondary and tertiary CÀH bonds. For example, a selectivity order of primary < secondary < tertiary C À H bonds has been observed for the extensively investigated carbene insertion catalyzed by rhodium complexes, [4,5] possibly because of the electron density order of primary < secondary < tertiary CÀH bonds, which renders primary CÀH bonds the least susceptible to attack by electrophilic rhodium-carbene intermediates.[5] By manipulating the steric or electronic properties of the metal catalysts, a selectivity for primary C À H bonds of alkanes comparable to that for secondary or tertiary C À H bonds was observed, [6] with the highest primary/secondary and primary/tertiary ratio per CÀH bond being 1.17:1.0[6b] and 1.0:0.9, [6c] respectively. Herein we report a highly selective primary CÀH bond functionalization by metal-catalyzed carbenoid insertion into the C À H bonds of alkanes (Scheme 1), which features a primary/secondary selectivity (that is, the primary/secondary ratio per C À H bond) of up to 11.4:1. We have also accomplished highly enantioselective functionalization of secondary C À H bonds with ee values of up to 93 % and product turnovers up to 6100 through metal-mediated carbenoid CÀH bond insertion reactions.Our studies in this work were inspired by previous work from the research groups of Callot [6a,b] and Suslick. [7] In the 1980s, Callot and co-workers reported that the primary C À H bond selectivity for the reaction of linear alkanes with ethyl diazoacetate (N 2 CHCO 2 Et, EDA) catalyzed by [Rh(por)I] (H 2 (por) = meso-tetraarylporphyrin) increases with the size o...

The chiral iridium porphyrin [Ir((-)-D(4)-Por*)(Me)(EtOH)] displays excellent reactivity and stereoselectivity towards carbene insertion to C-H and Si-H bonds, affording corresponding products in high yields (up to 96%) and high enantioselectivities (up to 98% ee).

Cu-catalyzed enantioselective alkylation of β-ketoesters using alcohols for in situ preparation of alkylating reagents is reported. A number of functionalized β-ketoesters containing a quaternary carbon stereocenter are obtained with up to 99% ee. The alkylation products derived from 2-substituted allylic alcohols or their corresponding iodides can then be converted to spirolactones, bi-spirolactones, and related chiral target products.

We successfully synthesized hydroxypropylcellulose (HPC) and methylcellulose (MC) in high yields from cellulose in 6 wt % NaOH/4 wt % urea aqueous solutions at 25°C. The cellulose derivatives were characterized with NMR, size exclusion chromatography/laser light scattering, gas chromatography (GC), ultraviolet, and solubility measurements in different solvents. According to the results of solution 13 C NMR and GC, the individual degree of substitution (DS; i.e., the average number of substituted hydroxyl groups in the monomer unit) at C-2 hydroxyl groups was slightly higher than the DS values at C-3 and C-6 hydroxyl groups for HPC and MC. In comparison with traditional systems, NaOH/urea aqueous solutions were proved to be a stable and more homogeneous reaction medium for preparing cellulose ether with a more uniform microstructure. The low limits for the average number of moles of the substituent groups per monomer unit and the DS value of water-soluble HPC were 1.03 and 0.85, respectively. MC (DS ϭ 1.48) had good solubility in both water and organic solvents, and the precipitation point occurred at about 67°C for a 2% (w/v) aqueous solution. In this way, we could provide a simple, pollution-free, and homogeneous aqueous solution system for synthesizing cellulose ethers.

The enantioselective trifluoromethylthiolation of β-ketoesters using chiral copper-boxmi complexes as catalysts is reported. A number of α-SCF3-substituted β-ketoesters have been obtained with up to >99% enantiomeric excess (ee), and the trifluoromethylthiolated products were then transformed diastereoselectively to α-SCF3-β-hydroxyesters with two adjacent quaternary stereocenters.