Yuri K. Grishin

Donor–Acceptor Cyclopropanes as Three‐Carbon Components in a [4+3] Cycloaddition Reaction with 1,3‐Diphenylisobenzofuran

Substituted cyclopropanes have found broad application in modern organic synthesis owing to the unique reactivity of the cyclopropane moiety. Cyclopropanes can often be considered as three-carbon analogues of C=C bonds. For example, alkenes and cyclopropanes react with strong electrophiles and various radicals. Both undergo the addition of hydrogen and can be oxidized at the a position. The reactivity of cyclopropanes with electron-withdrawing substituents is similar to that of electron-deficient alkenes. However, the cycloaddition reactions of alkenes and cyclopropanes are quite different. In particular, the thermal reactions of alkenes are represented mainly by [1+2], [3+2], and [4+2] cycloaddition processes; thermal [2+2] cycloaddition occurs in very specific cases only. In contrast, the most well known type of cyclopropane cycloaddition is the [2p + 2s] reaction with alkenes. As this reaction yields cyclopentanes, it can also be considered as a [2+3] cycloaddition. The scope of such [2+3] cycloaddition reactions has been expanded significantly through the use of donor–acceptor cyclopropanes. The presence of both electron-donating and electron-withdrawing substituents on the cyclopropane ring enables cycloaddition to various multiple bonds, including C=C, C=O, C=N, and C N bonds. The [4+3] cycloaddition of cyclopropanes with dienes (Scheme 1) has not been reported previously, although this

A RESOLUTION OF THE MONODENTATE P*-CHIRAL PHOSPHINE PBUTC6H4BR-4 AND ITS NMR-DEDUCED ABSOLUTE CONFIGURATION

Abstract Both enantiomers of the monodentate phosphine PBu t C 6 H 4 Br-4 were obtained in an enantiopure state by chromatographic separation of their diastereomeric adducts with a new homochiral ortho -palladated resolving agent derived from α- tert -Bu-substituted tertiary benzylamine. The conformation of the palladacycle and the absolute configuration of the phosphine were determined using 1 H NMR spectroscopy (including NOE technique) and confirmed by an X-ray diffraction study of both diastereomeric complexes. The enantiomers of the resolved phosphine were displaced from the individual diastereomers of the palladium(II) complexes with recovery of the starting resolving agent, and trapped in the form of binuclear coordination complexes of palladium(II).

First enantiopure phosphapalladacycle with planar chirality. X-Ray study of the racemic dimer and (Spl,SCSN)-diastereomer of its prolinate derivative

Abstract The first P , C -cyclopalladated complex with planar chirality was prepared by direct cyclopalladation of prochiral di- tert -butyl(ferrocenylmethyl)phosphine. Resolution of the racemic dimer was achieved through separation of its diastereomeric ( S )-prolinate derivatives. The palladacycle structure was confirmed by the 1 H NMR spectra of the dimer and its triphenylphosphine adduct and an X-ray diffraction study of the racemic dimeric complex. The absolute configuration of the planar chirality was determined by an X-ray diffraction investigation of one of two diastereomers of the ( S )-prolinate derivative.

P*-Chiral phosphapalladacycle as derivatizing agent for enantiomeric purity determination of α-amino acids by means of 31P NMR spectroscopy

Abstract A P*-chiral cyclopalladated complex was shown to be an efficient chiral derivatizing agent for enantiomeric excess determination of α-amino acids by 31 P NMR technique. The main advantages of this type of reagent are discussed.

Asymmetric exchange of cyclopalladated ligands with a high level of asymmetric induction: a new route to optically active phosphapalladacycles

Abstract The first example of an asymmetric CH bond activation with chirality transfer (up to 91% ee) from an enantiopure CN -palladacycle is described. This asymmetric version of cyclopalladated ligand exchange was elaborated in an aprotic medium using prochiral phosphines as substrates and an enantiopure benzylaminate palladacycle bearing a primary amino group and a bulky tert -Bu substituent on the side chain as the palladation agent.

Competition between sp3 and sp2 CH bonds in cyclopalladation of N-methyl-α-tert-butylbenzylamine

Intramolecular palladation of the (sp 3 )CH bond of a tert-butyl group of N-methyl-a-tert-butylbenzylamine can be achieved in competition with (sp 2 )CH bond activation where both possible reactions are equally suitable for five-membered palladacycle formation. Activation of the (sp 3 )CH bond occurs with PdCl4 2 assisted by a secondary amino group as a heterodonor center in a benzylamine ligand; regioselective activation of the (sp 2 )CH bond was achieved with PdI4 2 . To compare, cyclopalladation of the related tertiary amine occurs regioselectively to give ortho-palladated complex as the sole product. The structure of both regioisomeric complexes was confirmed by an X-ray study of their triphenylphosphine adducts. The conformational features of the two five-membered palladacycles is discussed on the base of the 1 H-NMR and X-ray data.

FIRST OPTICALLY ACTIVE P*-CHIRAL PHOSPHAPALLADACYCLE

Abstract The first cyclopalladated complex containing an asymmetric P*-donor atom in the phosphapalladacycle has been prepared in an enantiomerically pure state via resolution of diastereomeric (S)-prolinate derivatives of the racemic dimer. The absolute configuration of the P*-stereocenter (SP) and the geometric configuration of the palladium environment (Z) were determined by an X-ray diffraction investigation of the less soluble diastereomer of the (S)-prolinate adduct.

New one-pot method for the stereoselective synthesis of (E)-[β-(trifluoromethylsulfonyloxy)-alkenyl](Aryl) iodonium triflates

Abstract The reactions of reagent 1 with acetylenes leading to the alkenyl(aryl)iodonium triflates have been investigated. The results indicate that the very simple and efficient one-pot conversion of terminal alkynes into alkenyl(aryl)iodonium triflates described in this paper presents several advantages over the previously described procedure. The stereoselectivity of these reactions is discussed on the basis of physico-chemical evidence including IR, NMR spectroscopy and X-ray analysis. It is shown that these reactions are accompanied with anti-addition to afford (E)-[β-(trifyloxy)alkenyl](aryl) iodonium triflates in moderate to excellent yields. A possible mechanism is also discussed.

Unexpected Heterocyclization of Electrophilic Alkenes by Tetranitromethane in the Presence of Triethylamine. Synthesis of 3-Nitroisoxazoles

Novel reaction of tetranitromethane (TNM) with electrophilic alkenes in the presence of triethylamine yielding substituted 3-nitroisoxazoles was found and studied. Triethylamine increases the reactivity of TNM toward electrophilic alkenes promoting their heterocyclization, and the reactions proceed in an unusual way. A variety of alpha,beta-unsaturated aldehydes, ketones, esters, amides, phosphonates, and nitro and sulfur compounds was involved in the heterocyclization reaction, and a wide range of functionalized 3-nitroisoxazoles was obtained in good to high yields. The scope and limitations of the reaction and the mechanistic aspects are discussed.

Three-Component Heterocyclization of gem-Bromofluorocyclopropanes with NOBF4: Access to 4-Fluoropyrimidine N-Oxides

Novel three-component heterocyclization involving gem-bromofluorocyclopropanes, nitrosyl tetrafluoroborate, and a molecule of the solvent (nitrile) yielding previously unknown fluorinated pyrimidine N-oxides is described. A two-step synthetic approach to 4-fluoropyrimidine N-oxides from alkenes under mild conditions is developed using this reaction. Mechanistic aspects of the heterocyclization are discussed.