Enantioselective Addition of Chiral Organotitanium Derivatives to Aldehydes

Alkoxy- and aryloxy-organotitanium compounds 2–4 derived from (S)-2-methyl-1-butanol, (R)-2-butanol, (-)-menthol, quinine, cinchonine, and (S)-1.1′-binaphthol are added to aromatic aldehydes to give optically active alcohols 5–10 in enantioselectivities of up to 88% e. e., with nucleophilic transfer of methyl, phenyl, and 1-naphthyl groups. The Tables 1–3 list the effects of varying the reagents, the substrates, and the reaction conditions of the new asymmetric synthesis.     

Triphenylphosphine-Catalyzed Michael Addition of Alcohols to Acrylic Compounds

A facile triphenylphosphine-catalyzed Michael addition of alcohols to acrylic compounds was described. The reaction was carried out in open air at refluxing temperature in the presence of 10 mol% PPh3. Michael addition of saturated and unsaturated alcohols to acrylonitrile or acrylates has been examined. The reaction gave β-alkoxy derivatives with isolated yields of 5%-79%. PPh3 is cheaper and more stable than those trialkylphosphines previously used for the similar reactions, and the products can be easily separated from the reaction mixture via distillation.     

Diasteroselective Addition of Monoand Bis-Silylphosphines to Chiral Aldehydes

Abstract

The addition of silylphosphines to chiral aldehydes proceeds with high diastereoselectivity to give optically pure tertiary α -trimethylsiloxyalkylphosphines. The diastereomeric excesses of the addition products were achieved to 90–100%. The reaction of bis(trimethylsilyl)phenylphosphine with the acetonide of (R)-glyceraldehyde provides diastereomerically enriched tertiary bis(glyceryl)phosphines.     

Research on Asymmetric Michael Addition,Part II: Addition of the Menthone Imine of Ethyl Glycinate to Ethyl Acrylate Under PTC Conditions

Asymmetric Michael addition of (S)-menthone imine of ethyl glycinate to ethyl acrylate had been investigated under PTC conditions using solid base and different kinds of PT catalysts. The reaction gave adducts of enantiomeric excesses of 5–47%.     

Addition of alkynes to a gallium bis-amido complex: imitation of transition-metal-based catalytic systems

Acetylene, phenylacetylene, and alkylbutynoates add reversibly to (dpp‐bian)Ga–Ga(dpp‐bian) (dpp‐bian=1,2‐bis[(2,6‐diisopropylphenyl)‐imino]acenaphthene) to give addition products [dpp‐bian(R¹C?CR²)]Ga–Ga[(R²C?CR¹)dpp‐bian]. The alkyne adds across the Ga? N? C section, which results in new carbon–carbon and carbon–gallium bonds. The adducts were characterized by electron absorption, IR, and ¹H NMR spectroscopy and their molecular structures have been determined by single‐crystal X‐ray analysis. According to the X‐ray data, a change in the coordination number of gallium from three [in (dpp‐bian)Ga–Ga(dpp‐bian)] to four (in the adducts) results in elongation of the metal–metal bond by approximately 0.13 Å. The adducts undergo a facile alkynes elimination at elevated temperatures. The equilibrium between [dpp‐bian(PhC?CH)]Ga–Ga[(HC?CPh)dpp‐bian] and [(dpp‐bian)Ga–Ga(dpp‐bian) + 2 PhC?CH] in toluene solution was studied by ¹H NMR spectroscopy. The equilibrium constants at various temperatures (298≤T≤323 K) were determined, from which the thermodynamic parameters for the phenylacetylene elimination were calculated (ΔG°=2.4 kJ mol^?1, ΔH°=46.0 kJ mol^?1, ΔS°=146.0 J K^?1mol^?1). The reactivity of (dpp‐bian)Ga–Ga(dpp‐bian) towards alkynes permits use as a catalyst for carbon–nitrogen and carbon–carbon bond‐forming reactions. The bisgallium complex was found to be a highly effective catalyst for the hydroamination of phenylacetylene with anilines. For instance, with [(dpp‐bian)Ga–Ga(dpp‐bian)] (2 mol %) in benzene more than 99 % conversion of PhNH₂ and PhC?CH into PhN?C(Ph)CH₃ was achieved in 16 h at 90 °C. Under similar conditions, the reaction of 1‐aminoanthracene with PhC?CH catalyzed by (dpp‐bian)Ga–Ga(dpp‐bian) formed a carbon–carbon bond to afford 1‐amino‐2‐(1‐phenylvinyl)anthracene in 99 % yield.     

New Functional Diblock Copolymers Through Radical Addition of Mercaptans

1,2-Polybutadiene-block-poly(ethylene oxide)s were prepared by anionic polymerization and were subsequently modified by radical addition of ω-functional mercaptans (functional groups: carboxylic acid, amine, ethylene glycol, and fluorocarbon). The degree of functionalization of the products at full conversion of double bonds is 60–80%, and the molecular weight distribution is as narrow as that of the precursor polymer. The modified block copolymers are amphiphilic in nature and form complex aggregates in dilute aqueous solution.     

Addition polymers of aldehydes

The polymerization of aldehydes has played a considerable role in the progress of chain reaction polymerization and has significantly contributed to our knowledge of polymer science. Polyformaldehyde, as homopolymer and copolymer, plays an important role as a significant niche product in engineering plastics use. Higher aldehyde polymerization demonstrates the importance of stereospecificity and the ceiling temperature of polymerization. A discussion of haloacetaldehyde polymers is reserved for an upcoming article. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2293–2299, 2000     

Tetryl-Tetrylene Addition to Phenylacetylene

Phenylacetylene adds [Ar*GeH₂-SnAr’], [Ar*GeH₂-PbAr’] and [Ar'SnH₂-PbAr*] at rt in a regioselective and stereoselective reaction. The highest reactivity was found for the stannylene, which reacts immediately upon addition of one equivalent of alkyne. However, the plumbylenes exhibit addition to the alkyne only in reaction with an excess of phenylacetylene. The product of the germylplumbylene addition reacts with a second equivalent of alkyne and the product of a CH-activation, a dimeric lead acetylide, were isolated. In the case of the stannylplumbylene the trans-addition product was characterized as the kinetically controlled product which isomerizes at rt to yield the cis-addition product, which is stabilized by an intramolecular Sn–H–Pb interaction. NMR chemical shifts of the olefins were investigated using two- and four-component relativistic DFT calculations, as spin–orbit effects can be large. Hydride abstraction was carried out by treating [Ar'SnPhC=CHGeH₂Ar*] with the trityl salt [Ph₃C][Al(OC{CF₃})₄] to yield a four membered ring cation.     

Cyanoacetylene and Its Derivatives: XXXIV. Nucleophilic Addition of Tetrazole to Cyanoacetylenes

Nucleophilic addition of tetrazole to 4-hydroxy-4-alkyl-2-alkynonitriles and to 3-phenyl-2-propynonitrile occurred regiospecifically and afforded E-, Z-4-hydroxy-4-methyl-3-tetrazolyl-2-alkenonitriles and 3-tetrazolyl-3-phenyl-2-propenonitrile [20–40°C, 13–50 h, 4–15 wt% MOH (M = Na, K), THF (or DMSO)] in up to 69% yield. The attempt to perform cyclization of the hydroxy-containing adducts into iminodihydrofurans (KOH, ethanol, 23-25°C) resulted in vinyl nucleophilic substitution of the tetrazole moiety by an ethoxy group.     

Amberlyst-15 Catalyzed Addition of Phenols to α,β-Unsaturated Ketones

Amberlyst-15 has been used to catalyze regioselective additions of phenols to α,β-unsaturated ketones in yields of 20–90%. The reaction is superior to the analogous reaction employing concentrated sulfuric acid in affording greater yields and purer products with a minimum of laboratory operations.     

Diastereoselective Aldol Addition Using Boron Trichloride or Alkoxydichloroborane

Under carefully controlled conditions, boron trichloride or alkoxydichloroborane/ethyldiisopropylamine in CH₂Cl₂ can be used to effect diastereoselective aldol additions of ethyl ketones to saturated, α, β-unsaturated, or aromatic aldehydes. The C? C bond formation takes place with relative topicity ul (‘syn,’ configuration of the aldols), in selectivities ranging from 90 to 99% ds (Tables 1–3). Mechanistic aspects of the reaction are discussed.     

Organocatalytic Asymmetric 1,6‐Addition/1,4‐Addition Sequence to 2,4‐Dienals for the Synthesis of Chiral Chromans

A novel asymmetric organocatalytic 1,6‐addition/1,4‐addition sequence to 2,4‐dienals is described. Based on a 1,6‐Friedel–Crafts/1,4‐oxa‐Michael cascade, the organocatalyst directs the reaction of hydroxyarenes with a vinylogous iminium‐ion intermediate to give only one out of four possible regioisomers, thus providing optically active chromans in high yields and 94–99 % ee. Furthermore, several transformations are presented, including the formation of an optically active macrocyclic lactam. Finally, the mechanism for the novel reaction is discussed based on computational studies.     

Enantioselective Addition of Diethylzinc to Aromatic Aldehydes Catalyzed by New Chiral Oxazolidine Ligand

Abstract

The chiral oxazolidine ligand can catalyze the enantioselective addition of diethylzinc to aromatic aldehydes at room temperature with high enantioselectivity (98–99% ee). The conditions for this catalytic process are both mild and simple as compared with the same kind catalyst.     

Extremely Active Organocatalysts Enable a Highly Enantioselective Addition of Allyltrimethylsilane to Aldehydes

The enantioselective allylation of aldehydes to form homoallylic alcohols is one of the most frequently used carbon–carbon bond‐forming reaction in chemical synthesis and, for several decades, has been a testing ground for new asymmetric methodology. However, a general and highly enantioselective catalytic addition of the inexpensive, nontoxic, air‐ and moisture‐stable allyltrimethylsilane to aldehydes, the Hosomi–Sakurai 1 reaction, has remained elusive. 2 , 3 Reported herein is the design and synthesis of a highly acidic imidodiphosphorimidate motif (IDPi), which enables this transformation, thus converting various aldehydes with aromatic and aliphatic groups at catalyst loadings ranging from 0.05 to 2.0 mol % with excellent enantioselectivities. Our rationally constructed catalysts feature a highly tunable active site, and selectively process small substrates, thus promising utility in various other challenging chemical reactions.     

Addition of Allylindium Reagents to α-Iminotrifluoroethyl-phosphonates: Synthesis of CF3-Containing α-Aminoalkylphosphonates

Treatment of α-iminotrifluoroethylphosphonates with allylindium reagents in the presence of acetic acid afforded the corresponding CF₃ -containing α-aminoalkylphosphonates in high yields (83–97%) under mild conditions.     

Total Synthesis of Macrolactin A with Versatile Catalytic,Enantioselective Dienolate Aldol Addition Reactions

A highly convergent total synthesis of macrolactin A ( 1 ) utilizes modern asymmetric catalytic C–C coupling methods. The longest linear sequence in the route is 16 steps with an average yield of 86% per step. This total synthesis is valuable, because 1 , which has been shown to possess activity against HIV, is not readily accessible from its natural source, a taxonomically unclassified deep-sea bacterium.     

Rhodium-Catalyzed Addition of Organoboronic Acids to Aldehydes

Highly inert to ionic additions to aldehydes , aryl- and 1-alkenylboronic acids succumb to a catalytic variant mediated by a [Rh(acac)(CO)₂]–diphosphane complex in aqueous phase at 80–95°C to yield secondary alcohols [Eq. (a)]. A key step in the catalytic cycle is the transmetalation between the boron reagent and the rhodium complex. L_n=diphosphane (e.g. 1,1′-bis(diphenylphosphanyl)ferrocene); R=aryl, 1-alkenyl; R′=alkyl, aryl; acac=acetylacetonate.     

Reactivity of Nitroalkyl Anions Addition to Substituted Benzylidenecyanoacetates: Electrophilicity Parameters and Free Energy Relationships

The kinetics of the reactions of benzylidenecyanoacetates 1a–d (X = H, Me, OMe, and NMe₂) with nitroalkyl anions 2a–c have been studied in aqueous solution at 20°C. The second‐order rate constants are used to evaluate the electrophilicity parameter E of these series of Michael acceptors 1a–d according to the linear free enthalpy relationship log k (20°C) = s_N (E + N ). The measured E values were found to cover a domain of reactivity, ranging from −10.07 for the most reactive electrophile 1a (X = H) to −14.04 for the less electrophile 1d (X = NMe₂). Mayr's approach was found to correctly predict the rate constants for the reactions of these series of olefins 1a–d with the hydroxide ion in water and 50% water–50% acetonitrile at 20°C. Analysis of the kinetic measurements using the Brönsted relationship shows that β_nuc values remain remarkably constant for changes in the nature of the substituent X. A notable finding of this work is perhaps provided by the observed large changes in the electrophilicity parameter E on going from benzylidenecyanoacetates 1 to their analogues benzylidenemalonates 3 (ΔE ∼ 9.06–10.48), whereas the replacement of second CO₂Et group by the CN group in 1 to give benzylidenemalononitriles 4 has little effect on electrophilic reactivity, i.e., ΔE ∼ 0.65–0.95. This abnormal pattern in the E values has been attributed to the resonance interaction and salvation effects. On the other hand, the effect of benzylidenecyanoacetate substituents on the electrophilic reactivity was examined quantitatively on the basis of the electrophilicity parameter E , leading to linear correlation of E with Hammett–Brown substituent constants (). More importantly, the four electrophiles have comparable log k _o values, which are located at a relatively low level, i.e., log k _o ≤ 4–5, in the intrinsic reactivity scale.     

Zur oxidativen Addition von 1-Halogenalk-1-inen – Synthese und Struktur von Phenylalkinylpalladium-Komplexen

On the Oxidative Addition of 1-Halogenalk-1-ynes – Synthesis and Structure of Phenylalkynylpalladium Complexes [Pd(PPh₃)₄] ( 2 ) reacts with IC≡CPh and ClC≡CPh in the sense of an oxidative addition to give trans-[Pd(C≡CPh)X(PPh₃)₂] (X = I: 3 a , X = Cl: 3 b ). As side products trans-[PdX₂(PPh₃)₂] (X = I: 4 a , X = Cl: 4 b ; < 10%) and PhC≡C–C≡CPh ( 5 ; X = I: ca 30%, X = Cl: < 4%) are formed. 3 a and 3 b were characterized by NMR (¹H, ¹³C, ³¹P) and IR spectroscopies as well as by X-ray single-crystal structure analyses. In the crystals of 3 a and 3 b isolated molecules were found. The Pd–C≡C–Ph unit is linear in 3 a and approximately linear in 3 b [Pd–C≡C 174.2(6)°, C≡C–C 179,0(7)°].     

Iodine-Catalyzed Addition of Methyl Thioglycolate to Chalcones

Abstract

A series of novel β-mercapto carbonyl compounds (3a–z), methyl 2-(3-oxo-1,3-diarylpropylthio)acetate, were synthesized and characterized via iodine-catalyzed addition of methyl thioglycolate to chalcones (1a–z).

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