Martin Kotora

On the Mechanism of Asymmetric Allylation of Aldehydes with Allyltrichlorosilanes Catalyzed by QUINOX, a Chiral Isoquinoline N-Oxide

Allylation of aromatic aldehydes 1a-m with allyl- and crotyl-trichlorosilanes 2- 4, catalyzed by the chiral N-oxide QUINOX (9), has been found to exhibit a significant dependence on the electronics of the aldehyde, with p-(trifluoromethyl)benzaldehyde 1g and its p-methoxy counterpart 1h affording the corresponding homoallylic alcohols 6g, h in 96 and 16% ee, respectively, at -40 degrees C. The kinetic and computational data indicate that the reaction is likely to proceed via an associative pathway involving neutral, octahedral silicon complex 22 with only one molecule of the catalyst involved in the rate- and selectivity-determining step. The crotylation with (E) and (Z)-crotyltrichlorosilanes 3 and 4 is highly diastereoselective, suggesting the chairlike transition state 5, which is supported by computational data. High-level quantum chemical calculations further suggest that attractive aromatic interactions between the catalyst 9 and the aldehyde 1 contribute to the enantiodifferentiation and that the dramatic drop in enantioselectivity, observed with the electron-rich aldehyde 1h, originates from narrowing the energy gap between the (R)- and (S)-reaction channels in the associative mechanism (22). Overall, a good agreement between the theoretically predicted enantioselectivities for 1a and 1h and the experimental data allowed to understand the specific aspects of the reaction mechanism.

Synthesis of telechelic dienes from fluorinated α,ω-diiodoalkanes. Part I. Divinyl and diallyl derivatives from model I(C2F4)nI compounds

Abstract The synthesis of five fluorinated non-conjugated dienes from commercially available α,ω-diiodoperfluoroalkanes is described. Preparation of the fluorinated divinyl derivatives H2C=CH(CF2)nCH=CH2 (n = 2, 4, 6) (2,2, 2,4 and 2,6) was effected by ethylenation of these diiodinated compounds in various ways followed by dehydroiodination in ethanolic potassium hydroxide. Allyl diolefines, H2C=CHCH2(CF2)nCH2CH=CH2 (4,4 and 4,6) were produced by the α,ω-bis-telomerization of allyl acetate followed by deiodoacetoxylation in the presence of zinc. The diacetate precursors 3,4 and 3,6 of the respective diallyls 4,4 and 4,6 were obtained rather than diacetate 3,2 because of the eventual decomposition of α,ω-diiodoperfluoroethane by β-scission. These five fluorinated non-conjugated dienes have been characterized by 1H, 13C and 19F NMR spectroscopy.

NOVEL TYPE OF CARBOZIRCONATION REACTION OF ALKYNES

Abstract Novel type of carbozirconation reaction of alkynes is reported. Treatment of zirconocenealkyne complexes, zirconacyclopentenes, or zirconacyclopentadienes with allylic compounds gave allylzirconation products of alkynes. Carbozirconation of alkynes with zirconacyclopentenes or zirconacyclopentadienes involved β,β′-C-C bond cleavage reaction of zirconacycles. Reactions of zirconacyclopentenes with homoallyl bromides afforded allylcyclopropane derivatives as carbozirconation products.

Preparation of 1,2,3-trisubstituted cyclopentadienes and tetrahydroindene derivatives from zirconacyclopentenes

Abstract 1,2,3-Trisubstituted cyclopentadienes and tetrahydroindene derivatives were prepared by a one-step reaction from zirconacyclopentene complexes, which are easily prepared from alkynes and EtMgBr (or ethylene) and Cp 2 ZrCl 2 . Reaction of zirconacyclopentenes with phthaloyl chlorides afforded intramolecular Michael addition reaction products. The structure of one of the products was determined by X-ray study.

Copper-catalyzed addition of perfluoroalkyl iodides to unsaturated alcohols and transformation of the addition products

Abstract Iodoperfluoroalkyl alcohols R F CH 2 CHI(CR 2 ) n OH (R F = C 6 F 13 ; R = H, CH 3 ; n = 1–3, 9) have been readily prepared in high yield by the addition of perfluoroalkyl iodides R F I to allylic and other unsaturated alcohols at 120 °C in the presence of a catalytic amount (10% mol) of metallic copper powder. The dibenzoyl peroxide-induced reaction gave lower yields of the addition products in most cases. The chemical changes of iodoperfluoralkylated alcohols to epoxides and alcohols are described. A discussion of the by-products obtained and of the reaction mechanism is provided.

Inter‐ or Intramolecular Carbometalation of Nonactivated Alkynes by Zirconacyclopentanes in the Presence of Copper Chloride

Five- and six-membered carbocyles 2 and 3 can be obtained from zirconacyclopentanes of type 1 by a novel carbometalation with nonactivated alkynes in the presence of CuCl (see reaction scheme).

Cross coupling-conjugate addition reaction of zirconacyclopentadienes with 3-iodopropenoates

Abstract Copper-mediated reaction of zirconacyclopentadienes with iodopropenoates afforded penta- and hexasubstituted cyclopentadienes.

Addition of tetrachloromethane to halogenated ethenes catalyzed by transition metal complexes

Abstract 1:1 addition products in the reactions of tetrachloromethane with chloroethene, 1,1-dichloroethene, chlorotrifluoroethene and 1,1-dichlorodifluoroethene under catalysis by copper(I)—n-butylamine complex were obtained in high yields (60–97%). 1,2-Dichloroethenes and 1,2-dichlorodifluoroethene gave moderate yields of 1:1 adducts (10–21%) because of the steric effect of the bulky chlorine atoms attached to the carbon—carbon double bond. The formation of byproducts (dehydrochlorinated and reductively dehalogenated) in small amounts was observed when basic amines were used as ligands in copper(I)-catalyzed additions. RuCl2(PPh3)3 catalyst was selective and efficient in addition reactions of chloroethene and dichloroethene (86 and 89% yield of 1:1 adducts), but was inactive in the reaction of chlorotrifluoroethene. A palladium(0)—phosphine complex was completely inactive in all the reactions studied. The formation of byproducts, including 2:1 adducts, is discussed.

Efficient and diastereoselective synthesis of (+)-Goniobutenolide A via palladium-catalyzed ene-yne cross coupling-lactonization cascade

Abstract (+)-Goniobutenolide A was synthesized in six steps in 21.4% overall yield from (R)-mandelic acid via Pd-catalyzed ene-yne cross coupling-lactonization cascade with essentially complete control of the exocyclic alkene geometry.

A Novel Bifunctional Allyldisilane as a Triple Allylation Reagent in the Stereoselective Synthesis of Trisubstituted Tetrahydrofurans

Three for the price of two: A bifunctional allyldisilane undergoes a two-step triple allylation sequence with pairs of aldehydes to give all-cis trisubstituted tetrahydrofurans in excellent enantio- and diastereoselectivity (see scheme). The first allylation step, which sets up the key stereogenic centres, is catalysed by a chiral Lewis base.