An Efficient Indium-Mediated Synthesis of α-Cyano-β-Ethylenic Secondary Alcohols in Water

Coupling of aldehydes with 3-bromo-1-cyano-1-propene, using indium in water, is a very convenient method to prepare α-cyano-β-ethylenic secondary alcohols.     

Herstellung und Reaktionen von 2-Nitro-3-acetoxy-1-propen

Zusammenfassung Die Herstellung von 2-Nitro-3-acetoxy-1-propen (IV) wurde verbessert. Eine neue Reaktion wurde gefunden beim Studium der Umsetzung von sauren Nitroverbindungen mit 2-Nitro-3-acetoxy-1-propen oder einer Vorstufe, 1,3-Diacetoxy-2-nitro-propan (III). 1,1-Dinitroäthan reagierte in Gegenwart von Basen mit III oder IV und ergab 2,2,4,6,6-Pentanitro-heptan. Ein Mechanismus dieser Reaktion wird aufgestellt und ihre allgemeine Anwendbarkeit durch Herstellung von anderen Polynitroverbindungen veranschaulicht.

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An improved procedure for the preparation of 2-nitro-3-acetoxy-1-propene was developed. A new reaction was discovered in studying the addition of acidic nitro compounds to 2-nitro-3-acetoxy-1-propene (IV) or its precursor 1,3-diacetoxy-2-propane (III). The addition of 1,1-dinitroethane to III or IV, in the presence of base gave 2,2,4,6,6-pentanitroheptane. A mechanism for this reaction was postulated and its generality shown by preparation of other polynitroalkanes.

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Herrn Prof. Dr.H. Bretschneider in Freundschaft gewidmet.     

On the regiochemistry of nucleophilic attack on 2-halo pi-allyl complexes. 4. The effect of silver acetate and nucleophile concentrations in competitive nucleophilic attack with malonate and phenoxide nucleophiles

2,3-Dibromo-1-propene or its allyl carbonate analogue are ionized under Pd catalysis to generate the 2-bromo Pd-pi-allyl complex (triphenylphosphine ligand), which alkylates with malonate nucleophile at the terminal position. The presence of acetate ion in the reaction mixture results in some malonate attack being redirected to the central carbon. The acetate ion can come from the ionization of 1-acetoxy-2-bromo-2-propene or by the addition of silver acetate to the reaction mixture. The addition of phenoxide ion to the reaction also causes the same regiochemical phenomena, although harder anions such as methoxide exert no such effect.     

Synthesis of 1-substituted (S)-4-acetoxy-1-penten-3-ones using (S)-lactic acid as a chiral source and their synthetic reactions

Ylide reaction of (S)-3-acetoxy-1-triphenylphosphoranylidene-2-butanone, derived from (S)-lactic acid, with aldehydes gives 1-substituted (S)-4-acetoxy-1-penten-3-one derivatives, which are shown to be transformed into useful chiral compounds by stereoselective reduction or the Johnson-Claisen rearrangement.     

Reactivity studies of 3,3-bis(trimethylsilyl)-2-methyl-1-propene in Lewis acid-catalyzed allylation reactions

Allylation reagents, which possess geminal bis-trimethylsilyl substitution, are readily prepared from E- or Z-alkenyl bromides. The reactivity of 3,3-bis(trimethylsilyl)-2-methyl-1-propene (1) is described and predominantly provides ene reactions with aldehydes to give alcohol 2 in the presence of BF3.OEt2. Alternatively, Sakurai allylation reactions of 1 are observed by using stronger Lewis acids in methylene chloride to exclusively yield E-trisubstituted alkenylsilanes 3.     

Palladium-catalyzed asymmetric [3 + 2] trimethylenemethane cycloaddition reactions

Transition-metal-catalyzed trimethylenemethane (TMM) [3 + 2] cycloadditions provide direct routes to functionalized cyclopentanes. This reaction has been shown to be a highly chemo-, regio-, and diastereoselective process. We report a palladium-catalyzed asymmetric [3 + 2] trimethylenemethane (TMM) cycloaddition between 3-acetoxy-2-trimethylsilylmethyl-1-propene and various di- and trisubstituted olefins. Yields of exo-methylenecyclopentane products range from 59 to 99%, and enantiomeric excesses range from 58 to 92% ee.     

New hybrid ligands with a trans-1,2-diaminocyclohexane backbone: competing chelation modes in palladium-catalyzed enantioselective allylic alkylation

Three new hybrid ligands with trans-1,2-diaminocyclohexane backbone have been synthesized from (1R,2R)-2-aminocyclohexylcarbamic acid tert-butyl ester (4), which is prepared through an indirect monoprotection of the diamine. The ligands are (1R, 2R)-N-2-[2-(dimethylamino)benzoyl]aminocyclohexyl-2-(diphenylphosph anyl)benzamide and its di-n-butylamino- and diphenylamino-derivatives (3a-c), which belong to formal P,N-type chelates with possible wide bite angles in the metal chelation. To evaluate the new hybrid ligands against well-known P,N- and P, P-chelates (1 and 2), they were employed in the palladium-catalyzed allylic alkylations between two standard racemic allylic acetates, 2-acetoxy-1,3-diphenyl-2-propene (14a) and 2-acetoxy-1, 3-dimethyl-2-propene (14b), and dimethyl malonate under different reaction conditions. The catalytic system with the new ligands showed good reactivity toward both the substrates with moderate enantioselectivities (up to 78% ee toward 14a and 80% ee toward 14b). Of particular note, dramatic changes in the sense and in the degree of the enantioselectivity were observed depending on the ligands and reaction conditions, which suggested a different chelation mode was competing with the supposed P,N-chelation mode. An X-ray crystal structure of a chelated palladium complex [Pd(3c)(eta(3)-PhCHCHCHPh)]PF(6) was obtained, which showed a P, O-chelation mode in which a carboxamide oxygen acted as the O-ligand. This is the first example of the enantioselective palladium-catalyzed allylic alkylation in which a P,O-chelated complex of a carboxamide group participated as the ligand group.     

P-stereogenic P/N hybrid ligands: a remarkable switch in enantioselectivity in palladium-catalyzed asymmetric allylation

Optically active P-stereogenic phosphine/oxazoline bidentate ligands (1) were prepared and applied to palladium-catalyzed allylic substitution of 1,3-diphenyl-1-acetoxy-2-propene with dimethyl malonate. The absolute configuration of the allylation product was remarkably switched by changing a palladium/ligand ratio between 1/1 and 1/2.     

New homochiral amino-phosphine ligands: application in asymmetric palladium catalyzed allylic alkylation

A new series of homochiral amino-phosphine ligands was prepared. The use of these ligands in the palladium catalyzed allylic alkylation of 1,3-diphenyl-1-acetoxy-2-propene with sodium malonate gave substitution products with up to 76% e.e. The enantioselectivity was largely dependent on the nitrogen substituent.     

Preparation of titanated alkoxyallenes from 3-alkoxy-2-propyn-1-yl carbonates and (eta(2)-Propene)Ti(O-i-Pr)(2) as an efficient ester homoaldol equivalent

3-Alkoxy-2-propyn-1-yl carbonates (2) react with a divalent titanium reagent (eta(2)-propene)Ti(O-i-Pr)(2) to afford titanated alkoxyallenes 1 which, in turn, react with aldehydes regiospecifically to provide the corresponding gamma-addition products in good to excellent yields, thus affording a convenient method for synthesizing gamma-hydroxy esters 3 and/or gamma-butyrolactones 4.     

Barbier-type diastereoselective allylation of alpha-amino aldehydes with an enantiopure 2-sulfinylallyl building block.

An optimized procedure for the diastereoselective allylation under aqueous Barbier conditions of a series of alpha-amino aldehydes with our new chiral building block (S(s))-3-chloro-2-(p-tolylsulfinyl)-1-propene [(S(s))-1a] to afford enantiomerically pure sulfinylamino alcohols in good yields and diastereoselectivites is reported. High levels of diastereoinduction can be achieved from alpha-amino aldehydes configurationally related to natural alpha-amino acids.     

Addition von aldehyden an aktivierte doppelbindungen,XXVII. Mitteilung : Ein einfacher weg zu 2-hydroxy-cyclopentenonen

A new, easy synthetic route to 2-hydroxy-3-alkyl-cyclopentenones starting from the thiazolium salt catalyzed addition of aldehydes to 1-acetoxy-3-buten-2-one is described.     

Funktionelle Derivate von Polynitroverbindungen

Zusammenfassung DieMichael-Kondensation des 2-Nitro-3-acetoxy-1-propens¹ ermöglichte die Darstellung neuer aliphatischer Polynitroverbindungen mit zusätzlichen funktionellen Gruppen. Von besonderem Interesse sind die Verbindungen mit dreigem-Dinitrogruppen in der Kette, die durch direkte Nitrierung derAci-Salze von Kondensationsprodukten des 2-Nitro-3-acetoxy-1-propens mitgem-Dinitroverbindungen erhalten wurden.Die Reaktionsbedingungen wurden ermittelt und die Struktur der neuen Verbindungen sichergestellt.

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The study of reaction products from 2-nitro-3-acetoxy-1-propene¹ byMichael reactions led to the preparation of new aliphatic polynitro compounds containing functional groups. Of particular interest are compounds containing threegem-dinitro groups in a chain that have been obtained by direct nitration of theaci-salts of the condensation products from 2-nitro-3-acetoxy-1-propene withgem-dinitrocompounds. The reaction conditions have been established and the structure of the new compounds elucidated.

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Herrn Professor Dr.Fritz Wessely zum 70. Geburtstag in dankbarer Verehrung gewidmet.     

Reaction of allylzinc reagents and zinc enolates of ketones with alpha-amidoalkylphenyl sulfones

Alpha-amidoalkylphenyl sulfones behave as N-acylimino equivalents in the reaction with functionalized allylzinc reagents. The addition products obtained using the zinc derivative of ethyl 2-(bromomethyl)acrylate can be readily transformed into alpha-methylene-gamma-lactams using different cyclization procedures. The allylzinc reagent obtained from 3-bromo-1-acetoxy-1-propene directly affords protected 1,2-amino alcohols with a preference for the anti stereoisomer, regardless of the structure of the alpha-amidoalkylphenyl sulfone employed. This procedure can be extended to the use of zinc enolates obtained from alpha-bromo ketones and leads to the synthesis of N-protected beta-amino ketones.     

The Reactivity of 3-bromo-2-trimethylsilyl-1-propene towards electrophiles A short synthesis of 2-substituted-4-trimethylsilylfurans

3-bromo-2-trimethylsilyl-1-propene 1c reacts with various electrophiles (aldehydes, a ketone, nitriles, terminal alkynes) in the presence of zinc to give functionnalized vinylsilanes. A three steps synthesis of 2-substituted-4-trimethylsilylfurans from 1c and a nitrile is described. Opening of epoxysilanes with cuprates gave an easy access to α-trimethylsilyl-alcohols.     

Stereo- and regioselectivity of Pd(0)/InI-mediated allylic additions to aldehydes and ketones. In situ generation of allylindium(III) intermediates from N-acylnitroso Diels-Alder cycloadducts and 1-amino-4-acetoxycyclopentenes

Acylnitroso Diels-Alder cycloadduct (11, 37, and 45)- and cyclopentenyl acetate (8 and 9)-derived allylindium(III) species were generated in situ from palladium(0) catalysts and indium(I) iodide, and the stereo- and regiochemistry of their additions to aldehydes and ketones were investigated. Solvent, catalyst, and ionic effects were examined for the reaction of N-acetyl cycloadduct (11) and benzyloxyacetaldehyde (10). The solvent mixture of THF/H(2)O with Pd(OAc)(2).PPh(3) catalysis was found to be optimal. The addition of N-acetyl cycloadduct to aliphatic aldehydes afforded products in good yields and high regio- and stereoselectivity, with the cis-1,4-isomers constituting 90-95% of the products. The reactions with N-Boc (37a) and N-methylcarbamate (37b) cycloadducts also gave the cis-1,4-products predominantly. The same regio- and stereoselectivity applied to the reactions of 4-acetoxy-1-(N-hydroxyphenyacetamido)cyclopentene (8). 4-Acetoxy-1-phenylacetamidocyclopentene (9), however, afforded trans-1,4-products exclusively. Mechanistic speculations involving chelated transition states are described.     

Diastereoselective allylation of aldehydes with an enantiopure 2-sulfinylallyl halide under environmentally friendly Barbier-type conditions

[reaction: see text] A simple, efficient, and diastereoselective zinc-promoted allylation of aldehydes with enantiopure (Ss)-3-chloro-2-(p-tolylsulfinyl)-1-propene [(Ss)-1] under aqueous Barbier conditions is described. The observed diastereoselectivity can be explained via an acyclic antiperiplanar transition state model.     

Stereoselective synthesis of 1,4-disubstituted 1,3-diene from aldehyde using organotitanium reagent

Organotitanium reagent generated from 1-t-butylthio-3-trimethylsilyl-1-propene condenses with aldehydes to give 1 -t-butylthio-(E,Z)-1,3-alkadienes in a single step via (E)-erythro-β-hydroxysilane in a highly regio- and stereoselective manner. 1,4-Dialkyl-1,3-diene is obtaind from the diene sulfide by cross coupling reaction with Grignard reagent in the presence of nickel catalyst. The utility of the method is illustrated by application to the synthesis of Spilanthol, a naturally occurring insecticide from Spilanthese olerancae in five steps.     

A case for enantioselective allylic alkylation catalyzed by palladium nanoparticles

Palladium nanoparticles (4 nm, fcc) were prepared through decomposition of [Pd2(dba)3] by H2 in the presence of a chiral xylofuranoside diphosphite. These particles catalyze the allylic alkylation of rac-3-acetoxy-1,3-diphenyl-1-propene with dimethyl malonate leading to an almost total conversion of the (R) enantiomer and almost no reaction with the (S). This gives rise to 97% ee for the alkylation product and a kinetic resolution of the substrate recovered with ca. 90% ee. This behavior was compared to that of a molecular catalyst at various dilutions, and the differences between the two systems are discussed. This is the first colloidal system shown to display such a high enantioselectivity besides the well-known Pt/cinchonidine system.     

Allylic ionization versus oxidative addition into vinyl C-X bonds by Pd with polyfunctional olefin templates

The chemoselectivity of activation by a (PPh3)4Pd catalyst on a series of small, olefin-based compounds that were substituted with a variety of allylic and vinylic functional groups was studied. Of particular note, the allylic acetate of 1-acetoxy-2-bromo-2-propene (7) was selectively ionized by Pd in the presence of a malonate nucleophile, while oxidative addition of the C-Br bond to Pd occurred exclusively in the presence of a boronic acid nucleophile. When the acetate nucleophile was used, no ionization of the acetate leaving group occurred at all, which was proven by the use of deuterium-labeled substrates (e.g., 11). This report demonstrates that the nucleophile interacts in some way with Pd prior to catalyst activation of the substrate. Certainly in the case of the malonate nucleophile, this is without precedent and contradicts the central dogma of how these proposed catalytic cycles operate.