Ionic liquid media resulted in more efficient regio- and stereoselective aminohalogenation of cinnamic esters

β-Amino functionalization of cinnamic Weinreb amides in ionic liquid

2-Ns-Protected β-amino Weinreb amides were synthesized by aminochlorination of α,β-unsaturated Weinreb amides in an ionic liquid, 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][NTf₂]). Processed without the use of metal catalysts or the need of an inert gas atmosphere, the presented process can be readily performed as a one-pot synthesis at room temperature. Moreover, the preparation has the distinct advantages of the use of 2-NsNCl₂ as an inexpensive and stable nitrogen/halogen source and the ionic liquid as a recyclable reaction media. Nine examples were examined, and modest to good isolated chemical yields (40–83%) were obtained.

A Metal-Free Protocol for Aminofunctionalization of Olefins Using TsNBr2

N,N-Dibromo-p-toluene sulfonamide (TsNBr2) has been found to be an effective reagent for various aminofunctionalization reactions. This reagent behaves both as an electrophilic bromine source as well as amine to react with olefins under different conditions to yield aminoether, imidazoline, diamine and amino bromine. The reaction proceeds rapidly under mild conditions with high regioselectivity. Olefins react with TsNBr2 in moist THF to form δ-amino ether at room temperature. Treatment of TsNBr2 with olefin in MeCN at room temperature produced imidazoline in high yield. Further modification of the reaction condition resulted in the development of a one-step procedure for the synthesis of N-acetyl,N'-tosyl diamine derivatives directly from olefin. When the olefin was treated with 2.4 mol equiv of TsNBr2 in the presence of K2CO3, N,N'-ditosyl diamine derivative was obtained in moderate yield. Instantaneous formation of aminobromine was observed when an olefin was treated with the reagent in dry CH2Cl2 at room temperature.

Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines

A new approach to the anticancer drug Velcade was developed by performing asymmetric borylation of an imine anchored with a chiral N-phosphinyl auxiliary. Throughout the 7-step synthesis, especially in the imine’s synthesis and in the asymmetric borylation reactions, operations and work-up were conducted in simple and easy ways without any column chromatographic purification, which defines the GAP (group-assisted purification) chemistry concept. It was found that the optically pure isomer (dr > 99:1) can be readily obtained by washing the crude mixture of the asymmetric borylation reaction with hexane; the chiral N-phosphinyl auxiliary can be easily recovered after deprotection is finished. Several other N-phosphinylimines were also investigated for the asymmetric borylation reaction. The absolute configuration of the borylation product was confirmed by single crystal X-ray diffraction analysis.

Lewis basic selenium catalyzed chloroamidation of olefins using nitriles as the nucleophiles

A Lewis base catalyzed chloroamidation of olefinic substrates was achieved using diphenyl selenide as the catalyst. The reaction conditions are mild and suitable for a wide range of substrates including those which are acid labile.

Approach to vicinal t-Boc-amino dibromides via catalytic aminobromination of nitrostyrenes without using chromatography and recrystallization

A 1.0 mol % amount of K(3)PO(4)·3H(2)O was found to catalyze aminohalogenation reaction of nitrostyrenes with N,N-dibromo-tert-butylcarbamate (t-Boc-NBr(2)) in a dichloroethane system. Good to excellent yields and complete regioselectivity have been achieved by taking advantage of the GAP workup without using traditional purification techniques such as column chromatography and recrystallization. Anew mechanism is proposed involving radical and ionic catalytic cycles and an intramolecular migration.

Highly regio- and stereoselective synthesis of alpha-(N-alkyl-N-p-toluenesulfonyl)-beta-bromo-ketones via Ni(OAc)2-catalyzed aminobromination of chalcones

The combinations of N-methyl-p-toluenesulfonamide/NBS and N-ethyl-p-toluenesulfonamide/NBS were found to be good nitrogen/halogen resources for the aminohalogenation of alpha,beta-unsaturated ketones in the presence of Ni(OAc)(2) as the catalyst for the synthesis of vicinal haloamino ketone derivatives. The introduction of N-alkyl groups to the nitrogen resources resulted in excellent regio- and stereoselectivity for both electron-donating and electron-withdrawing group-attached unsaturated ketone substrates. The structure of the resulting products has been unambiguously confirmed by X-ray crystal structure analysis.

Design and Synthesis of Pyridinium Chiral Ionic Liquids Tethered to a Urea Functionality

Nine chiral room-temperature ionic liquids (RTILs), which contain a chiral moiety and a urea functionality bonded to a pyridinium ring, have been designed and synthesized. The synthesis of these ionic liquids is concise and practical due to the commercial availability of the starting materials. These novel RTILs were readily prepared from 2-(aminomethyl)pyridine and amino acid ester derived isocyanates. We envision that these new chiral RTILs can serve as effective reaction media as well as chiral catalysts for asymmetric reactions, which are presently being investigated in our laboratory.

Design and synthesis of C-2 substituted chiral imidazolium ionic liquids from amino acid derivatives

[reaction: see text] A series of novel chiral ionic liquids (CILs) has been synthesized and fully characterized. The reaction of 1-methyl-2-imidazolecarboxaldehyde and chiral amino alcohols followed by reduction is key to the design of these new CILs. This is the first time that CILs have been synthesized by introducing chiral scaffolds on the C-2 position of the imidazolium cation of ILs. The simple and straightforward procedure resulted in CILs as colorless oils at room temperature in good yields.