Highly enantioselective alkylation of protected glycine diphenylmethyl (Dpm) amide 1 and Weinreb amide 10 has been realized under phase-transfer conditions by the successful utilization of designer chiral quaternary ammonium salts of type 4 as catalyst. Particularly, remarkable reactivity of the chiral ammonium enolate derived from 1b and 4c allowed the reaction with less reactive simple secondary alkyl halides with high efficiency and enantioselectivity. An additional unique feature of this chiral ammonium enolate is its ability to recognize the chirality of beta-branched primary alkyl halides, which provides impressive levels of kinetic resolution and double stereodifferentiation during the alkylation, allowing for two alpha- and gamma-stereocenters to be controlled. Combined with the subsequent reduction using LiAlH4 in cyclopentyl methyl ether (CPME), this system offers a facile access to structurally diverse optically active vicinal diamines. Furthermore, the optically active alpha-amino acid Weinreb amide 11 can be efficiently converted to the corresponding amino ketone by a simple treatment with Grignard reagents. In addition, reduction and alkylation of the optically active alpha-amino ketone into both syn and anti alpha-amino alcohols with almost complete relative and absolute stereochemical control have been achieved. With (S,S)- and (R,R)-4 in hand, the present approach renders both enantiomers of alpha-amino amides including Weinreb amides readily available with enormous structural variation and also establishes a general and practical route to vicinal diamines, alpha-amino ketones, and alpha-amino alcohols with the desired stereochemistry.

Palladium-catalyzed intramolecular cross-coupling reactions between aryl iodides and allyl moieties were successfully demonstrated in the presence of palladium catalyst, tri-o-tolylphosphine, a tertiary amine, and water. Several kinds of trans-2,4-disubstituted 1,2,3,4-tetrahydroquinolines were synthesized in 73-88% yields with excellent diastereoselectivities. This method was further applied to a large variety of substrates to form five-, six-, and seven-membered carbo- and heterocycles in good yields, regardless of the ring-containing atom, via microwave-assisted conditions.

The Stevens and Sommelet-Hauser rearrangements of ammonium ylides are known as useful transformations for organic synthesis because they convert a readily accessible CÀN bond into a new CÀC bond.[1] The Stevens rearrangement has been widely used for the asymmetric synthesis of aamino acid derivatives, [2,3] whereas the Sommelet-Hauser rearrangement is much less common because it usually competes with the [1,2] Stevens rearrangement.[4] For example, the base-induced rearrangement of carbonyl-stabilized ammonium ylides such as those derived from N-benzylic aamino esters almost exclusively undergoes the [1,2] Stevens rearrangement to give the a-benzylated amino acid derivatives. For these reasons, synthetic applications of the Sommelet-Hauser rearrangement and its asymmetric versions have been limited.[5] Herein, we report a unique example of a Sommelet-Hauser rearrangement of carbonyl-stabilized ammonium ylides that is not accompanied by the [1,2] Stevens rearrangement to a detectable extent.Recently, we reported that the [1,2] Stevens rearrangement of ammonium salt 1, which is derived from (2S)-N-(4-tert-butoxycarbonyl)benzyl proline tert-butyl ester, proceeds with a perfect level (greater than 99 %) of N-to-C chirality transfer to give the a-benzylated proline tert-butyl ester 2 (Scheme 1).[2b] However, when the rearrangement was performed in THF at À40 8C using potassium tert-butoxide (1.5 equiv) as a base, the Sommelet-Hauser rearrangement (concerted [2,3] sigmatropic process) proceeded exclusively to give the corresponding a-aryl proline [6] derivative 3 in 96 % yield. The 1 H NMR analysis of 3 showed a new singlet peak from benzylic methyl protons (d = 2.27 ppm in CDCl 3 ), three proton signals from aromatic protons, and the disappearance of the benzylic methylene protons. The enantiomeric excess was determined to be greater than 99 % by chiral HPLC analysis after reduction of 3 to the amino alcohol with lithium aluminum hydride.[7] The R configuration of 3 was assigned by analogy with the reported examples of [2,3] Stevens rearrangement of proline-derived ammonium salts. [2d, e]

A series of (2,7-disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) (2) has been readily prepared in situ by treatment of the requisite 2,7-disubstituted-1,8-biphenylenediol (1) with Me3Al (2 equiv) in CH2Cl2 at room temperature; this primarily relies on the successful establishment of a new synthetic procedure of 1 starting from inexpensive m-anisidine. Evaluation of 2 as a bidentate organoaluminum Lewis acid has been performed by the reduction of ketonic substrates using Bu3SnH as a hydride source in comparison to the conventional monodentate Lewis acid dimethylaluminum 2,6-xylenoxide (11), uncovering the significantly high activation ability of 2 toward carbonyl. Particularly, (2,7-dimethyl-1,8-biphenylenedioxy)bis(dimethylaluminum) (2a) exerted the highest reactivity, which has also been emphasized in the Mukaiyama aldol reaction. The structure of the bidentate Lewis acid 2 was unambiguously determined by single-crystal X-ray diffraction analysis of 2g possessing a bulky 3,5-di-tert-butylphenyl substituent, revealing the rigid dimeric assembly in the solid state. The double electrophilic activation of carbonyl substrate by 2a has been supported by low-temperature 13C NMR analysis as well as theoretical study using the Gaussian 98 program. Moreover, unique stereoselectivity has been observed in the 2a-promoted Mukaiyama Michael addition, and highly chemoselective functionalization of carbonyl compounds in the presence of their acetal counterparts has been realized using 2a. Finally, the effectiveness of 2a for the activation of ether functionality has been demonstrated in the Claisen rearrangement of allyl vinyl ethers.

The intermolecular aromatic substitution of N,N‐disubstituted anilines with diazo esters is achieved under mild conditions in the presence of a catalytic amount of copper(II) triflate (up to 89 % yield). The scope and limitations regarding substrates, diazo esters, and ligands in this reaction are described.

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a b s t r a c tPhotoinduced electron transfer (PET) reactions promoted by 2-aryl substituted 1,3-dimethylbenzimidazolines (Ar-DMBIH) were investigated. Excited states of Ar-DMBIH, formed by irradiation using light above 360 nm, initiate PET reductions of various organic substrates, including transformations of epoxy ketones to aldols, free radical rearrangements such as the Dowd-Beckwith ringexpansion and 5-exo hexenyl cyclization, deprotection of N-sulfonyl-indols, and allylation of acyl formates. In these processes, Ar-DMBIH possessing 1-naphthyl, 2-naphthyl, 1-pyrenyl and 9-anthryl substituents formally act as two electron and one proton donors while the hydroxynaphthyl substituted derivative serves as a two electron and two proton donor. On the basis of the results of absorption spectroscopy studies, cyclic voltammetry and DFT calculation, a mechanistic sequence for these reduction reactions is proposed that involves initial photoexcitation of the aryl chromophore of the Ar-DMBIH followed by single electron transfer (SET) to the organic substrate to generate the radical cation of benzimidazoline and the radical anion of the substrate.

Unter nahezu vollständigem Chiralitätstransfer gelang die Alkylierung am N‐Terminus kleiner Schiff‐Basen‐aktivierter Peptide unter milden Phasentransferbedingungen und mit fein abgestimmten chiralen quartären Ammoniumsalzen als Katalysatoren. Durch wiederholte Verlängerung und Alkylierung am N‐Terminus sind so nichtnatürliche Oligopeptide mit hoher Selektivität zugänglich (siehe Bild).