<i>Erythro</i>‐Selective Aldol‐Type Addition of Titanated Aldehyde‐Hydrazones

Reetz, Manfred T.; Steinbach, Rainer; Keßeler, Kurt

doi:10.1002/anie.198208641

Cited by 27 publications

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“…Synthesis and Reactivity of Hydrazido(1-) and Hydrazido(2-) Titanium dpma Complexes. Only a few titanium complexes bearing multiple hydrazido(1-) ligands have been fully characterized. 13b,s,t For example, Leigh and co-workers reported the bis[η 2 -hydrazido(1-)] complex of titanium Ti(NMeNMe 2 ) 2 Cl 2 synthesized from trimethylhydrazine and titanium chloride. As shown in Scheme , treatment of a room-temperature solution of Ti(NMe 2 ) 2 (dpma) ( 1 ) with excess 1-aminopiperidine resulted in the generation of an unusual bis[η 2 -hydrazido(1-)] complex Ti(NHNC 5 H 10 ) 2 (dpma) ( 5 ).…”

Section: Resultsmentioning

confidence: 99%

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Titanium Hydrazido and Imido Complexes: Synthesis, Structure, Reactivity, and Relevance to Alkyne Hydroamination

2004

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Treatment of Ti(NMe(2))(2)(dpma) (1) with aniline results in the protonation of the dimethylamido ligands, which are retained as dimethylamines, and generation of a titanium imido complex Ti(NPh)(NHMe(2))(2)(dpma) (2) in 94% yield. The monomeric imido 2 is converted to the reactive dimeric micro-imido [Ti(NPh)(dpma)](2) (3) on removal of the labile dimethylamine donors. The dimer 3 is converted to monomeric terminal imido complexes in the presence of added donors, e.g., 4,4'-di-tert-butyl-2,2'-bipyridine (Bu(t)-bpy) and DME. Compounds 1-3 exhibit the same rate constant for 1-phenylpropyne hydroamination by aniline and are all kinetically competent to be involved in the catalytic cycle. Attempts to use 1 as a catalyst for hydroaminations involving 1,1-dimethylhydrazine resulted in only a few turnovers under the best conditions. Consequently, the chemistry of 1 with hydrazines to generate hydrazido complexes was scrutinized for comparison with the imido species. Through these studies, titanium hydrazido complexes including Ti(eta(2)-NHNC(5)H(10))(2)(dpma) (5), Ti(eta(2)-NHNMe(2))(2)(dpma) (6), and [Ti(micro:eta(1),eta(2)-NNMe(2))(dpma)](2) (7) were characterized. In addition, a terminal hydrazido(2-) complex was available by addition of Bu(t)-bpy to 1 prior to 1,1-dimethylhydrazine addition, which provided Ti(eta(1)-NNMe(2))(Bu(t)-bpy)(dpma) (8). Compound 8 was structurally characterized and compared to Ti(NPh)(Bu(t)-bpy)(dpma) (4b), an imido derivative with the same ancillary ligand set. Compound 8 has a nucleophilic beta-nitrogen consistent with a hydrazido(2-) formulation, as determined by reaction with MeI to form the ammonium imido complex [Ti(NNMe(3))(Bu(t)-bpy)(dpma)]I (9). Analogous pyridinium imido complexes [Ti(N-1-pyridinium)(Bu(t)-bpy)(dpma)](+) (10) are available by addition of 1-aminopyridinium iodide to 1. From the investigations, some conclusions regarding the activity of titanium pyrrolyl complexes in hydroamination were drawn. The lack of conversion of the bis[micro-hydrazido(2-)] 7 to monomeric species in the presence of donor ligands is put forth as one explanation for the poor hydrazine hydroamination activity of 1. This problem was combated in the synthesis of Ti(NMe(2))(2)(dap)(2), which is an active catalyst for hydrazine hydroamination of alkynes.

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Section: Resultsmentioning

confidence: 99%

“…More common are reports of hydrazido(1-) complexes of titanium . Fully characterized complexes in this genre usually have incorporated cyclopentadienyl, tris(pyrazolyl)borate, or halide supporting ligands …”

Section: Introductionmentioning

confidence: 99%

Titanium Hydrazido and Imido Complexes: Synthesis, Structure, Reactivity, and Relevance to Alkyne Hydroamination

2004

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“…Ti(O- i -Pr) 4 , benzaldehyde, propanal, and butanal were distilled and stocked under argon. ClTi(O- i -Pr) 3 was prepared from Ti(O- i -Pr) 4 and TiCl 4 according to the procedure described in the literature and stocked as a 2.0 M of ethereal solution under argon. i -PrMgBr and i -PrMgCl were prepared from commercial magnesium turnings and 2-bromo- or 2-chloropropane according to the conventional procedure as a 1.1−1.8 M of ethereal solution, titrated, and stocked under argon.…”

Section: Methodsmentioning

confidence: 99%

Intramolecular Nucleophilic Acyl Substitution Reactions Mediated by XTi(O-i-Pr)₃ (X = Cl, O-i-Pr)/2i-PrMgBr Reagent. Efficient Synthesis of Functionalized Organotitanium Compounds from Unsaturated Compounds

et al. 1996

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Treatment of acetylenic or olefinic carbonates and esters with a low-valent titanium reagent diisopropoxy(η2-propene)titanium (1), readily generated by the reaction of Ti(O-i-Pr)4 or ClTi(O-i-Pr)3 with 2i-PrMgX, resulted in an intramolecular nucleophilic acyl substitution (INAS) reaction to afford organotitanium compounds having a carbonyl functional group, in good to excellent yields. Thus, the treatment of alkyl alkynyl carbonates 2 or alkyl alkenyl carbonates 4 with 1 gave organotitanium compounds having a lactone and/or ester group. Similarly, alkyl alkynoates 10 or alkynyl esters 14 of carboxylic acids reacted with 1 to give organotitanium compounds having a cyclic or acyclic ketone group, respectively. Thus, the reaction provides, after hydrolysis, five- or six-membered α-alkylidene lactones and/or α,β-unsaturated esters from 2, γ-butyrolactone derivatives from 4, five- or six-membered α-alkylidene cyclic ketones from 10, and acyclic α,β-unsaturated ketones 15 from 14. In all cases, the yields are excellent and the generation of the organotitanium compounds was confirmed by deuterolysis. The organotitaniums 6 and 11c reacted smoothly with iodine to afford 2-(iodomethyl)-4-butanolide (9) and α-[iodo(trimethylsilyl)methylidene]cyclopentanone, respectively. The organotitanium compounds obtained here also reacted with aldehydes to give the corresponding adducts, thus opening up a new access to substituted α,β-butenolides from 2, to γ-butyrolactones from 4, and to the corresponding tetrasubstituted furan from 10 and 14.

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“…234 Diastereoselection is possible, since (E)-alkenyl acetals give the erythro-isomer, and threo-diastereoisomers result from rearrangement of (2)-alkenyl acetals. 236 Titanium derivatives of aldehyde hydrazones participate in highly erythroselective reactions with aldehydes, giving a method for the diastereoselective cross-coupling of two aldehydes (Scheme 53). 236 The diastereoselection is also observed with ketone hydrazones.…”

Section: Mementioning

confidence: 99%

Aldehydes and ketones

EYLEY¹

1985

General and Synthetic Methods

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Oxidative Methods.-Further studies of oxidations using sodium hypochlorite in glacial acetic acid have shown that secondary alcohols may be oxidized to ketones in the presence of primary a1cohols.l In one example where epimerization of the ketonic product was possible, isomerization was not observed under the reaction conditions. The easily stored calcium hypochlorite also oxidizes secondary alcohols to ketones.2 Yields are high in dichlorornethane or acetronitrile containing acetic acid. cr-Diols are cleaved oxidatively to aldehydes or ketones, depending on the starting materiaL3 A hypochlorite may be used as an oxidant for secondary alcohols in various solvents (dichloromethane, carbon tetrachloride, ether, or ethyl acetate) in the presence of catalytic amounts of the hypochlorite form of the commercial resin IRA goo.* This method, allowing a non-aqueous work-up to be employed, may prove advantageous for the preparation of water-soluble products. Sodium bromate, in the presence of cerium(1v) ammonium nitrate or cerium(1v) sulphate, also oxidizes secondary alcohols in preference to primary alcohol^.^The uses of the versatile oxidant pyridinium chlorochromate have been reviewed.6 Pyridinium chlorochromate has been used for the oxidation of methyl 5-hydroxypentanoate to the aldehyde,' an intermediate useful in the synthesis of leukotrienes, and the same reagent oxidatively cleaves secondary vicinal diols to the corresponding aldehydes.8 The reactivity of the chlorochromate ion as an oxidant can be influenced by the counter-ion. For example, the 4-dimethylaminopyridinium salt is a mild, selective reagent for the oxidation of allylic and benzylic alcohols. Pyridinium fluorochromate oxidizes primary and secondary alcohols to aldehydes and ketones respectively in dichloromethane solution, and shows a less pronounced acidity compared with the chloro-

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Erythro‐Selective Aldol‐Type Addition of Titanated Aldehyde‐Hydrazones

Abstract: A Scheme 1 . 3-9: a , X = CH2, R' = H, R 2 = CH,; b , X = 0, Angew. Chem. Inr. Ed. Engl. 21 (1982) No. 11 0

Cited by 27 publications

References 3 publications

Titanium Hydrazido and Imido Complexes: Synthesis, Structure, Reactivity, and Relevance to Alkyne Hydroamination

Titanium Hydrazido and Imido Complexes: Synthesis, Structure, Reactivity, and Relevance to Alkyne Hydroamination

Intramolecular Nucleophilic Acyl Substitution Reactions Mediated by XTi(O-i-Pr)₃ (X = Cl, O-i-Pr)/2i-PrMgBr Reagent. Efficient Synthesis of Functionalized Organotitanium Compounds from Unsaturated Compounds

Aldehydes and ketones

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Erythro‐Selective Aldol‐Type Addition of Titanated Aldehyde‐Hydrazones

Abstract: A Scheme 1 . 3-9: a , X = CH2, R' = H, R 2 = CH,; b , X = 0, Angew. Chem. Inr. Ed. Engl. 21 (1982) No. 11 0

Cited by 27 publications

References 3 publications

Titanium Hydrazido and Imido Complexes: Synthesis, Structure, Reactivity, and Relevance to Alkyne Hydroamination

Titanium Hydrazido and Imido Complexes: Synthesis, Structure, Reactivity, and Relevance to Alkyne Hydroamination

Intramolecular Nucleophilic Acyl Substitution Reactions Mediated by XTi(O-i-Pr)3 (X = Cl, O-i-Pr)/2i-PrMgBr Reagent. Efficient Synthesis of Functionalized Organotitanium Compounds from Unsaturated Compounds

Aldehydes and ketones

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Intramolecular Nucleophilic Acyl Substitution Reactions Mediated by XTi(O-i-Pr)₃ (X = Cl, O-i-Pr)/2i-PrMgBr Reagent. Efficient Synthesis of Functionalized Organotitanium Compounds from Unsaturated Compounds