Aldehydes titanium isopropoxide

It is possible to exclusively methylenate a ketone in the presence of an aldehyde by precomplexing the aldehyde (e.g. 76) with Ti(NEt2)4, followed by treatment with the usual methylene zinc/TiCU reagent (equation 17). Takai also studied the chemoselective methylenadon of aldehydes (78) in the presence of ketones, and found the use of diiodomethane, zinc and titanium isopropoxide or trimethylaluminum to be effective (equation 18). ... 

It is advantageous to utilize either titanium isopropoxide or trimethylaluminum complexes with aldehydes in general, because pinacol-coupled diols form with the Zn/CH2Br2/riG4 systems as minor side products. No evidence of Simmons-Smith-type side products was observed with any of the methylena-tion reagents. Additional examples of the reaction with aldehydes are presented in Table 11. 

A number of methods to increase the thermal stability of Kdbrich reagents have centered around replacement of the lithium counterion normally present with a variety of transition metals, chiefly titanium, hafnium and copper." For example, the reagent derived from transmetalladon of lithium dichlorometh-ane with titanium isopropoxide could be reacted with various ketones and aldehydes to afford halohydrin adducts in good yields at temperatures as high as 0 °C. Competition experiments established the chemoselectivity of this reagent (Scheme 14). The direct activation of severid allylic halides has been accomplished with tin and chromium ° reagents (equation 26). Transmetallation of an alkyllead precursor has also been noted. 

The lithiation of ethyl allyl sulfide followed by transmetallation with titanium isopropoxide engenders an allyltitanium reagent formulated as (26 Scheme 8). This and related reagents add to aldehydes or ketones to afford hydroxy sulfides, which are converted to epoxides as shown. The power of this method for the stereoselective generation of even trisubstituted epoxides is evident from Scheme 8 and equation (18). Reagent (26a), prepared as shown in Scheme 8a, undergoes addition to ketone (26b) to afford product exclusively resulting from chelation-controlled diastereofacial addition (as a mixture of epimers at the position shown). ... 

Subsequently, Balan and Adolfsson et al. employed chiral quinuchdine derivatives as catalysts in the asymmetric one-pot three-component aza-MBH reaction of aryl aldehydes, tosylamide and alkyl acrylates or acrylonitrile. A sterically non-hindered tricyclic derivative of quinidine (141) was the most efficient catalyst in transferring its chiral information. High conversions were ensured by using a catalytic amount of titanium isopropoxide and by the addition of molecular sieves (4 A). The corresponding adducts 218 and 219 were obtained in good yields with up to 74% ee (Scheme 1.84). ... 

Balan and Adolfsson have reported that a-methylene-p-amino acid derivatives 267 are readily formed in a three-component one-pot MBH reaction of aryl aldehydes, sulfonamides and activated alkenes. The reaction is catalyzed efficiently by titanium isopropoxide [Ti-(OPr%] and 3-hydroxyquinuclidine (3-HQD) in the presence of molecular sieves, to afford the corresponding adducts in high yields with good to excellent chemoselectivities (Scheme 2.151). ... 

To 0.2 mmol of a solution of (/ )-(+)-l,l -bi(2-naphthol)titanium isopropoxide in toluene in a Schlenk tube were added 0.4 mmol of the aldehyde and 0.45 mmol of allyltributyltin. The solution was stirred at 20 °C over 20 hours, quenched with 1 mL of water, 10 mL of ether was added to the mixture, then the organic layer was washed with water and was dried over MgS04. After evaporation of the solvent, the product was purified by chromatography on silica gel (pentane/ether). 

The interactions between the chiral Schiff bases being derivatives of 2-aminoalcohols and substituted salicylic aldehydes and titanium (IV) isopropoxide [33] have been monitored by aH NMR spectroscopy.81... 

In nitro aldehydes both the nitro group and the aldehyde group are readily reduced by catalytic hydrogenation. It may be difficult, if not impossible to hydrogenate either function separately. More dependable methods are reduction by alane [787] or by isopropyl alcohol and aluminum isopropoxide Meerwein-Ponndorf) [788] to nitro alcohols, and by stannous chloride [789, 790], titanium trichloride [590] or ferrous sulfate [218] to amino aldehydes Procedure 38, p. 214). 

Reactions of lithium and titanium compounds 2, generated in situ by deprotonation of alkynylsilanes with tm-butyllithium, followed by addition of titanium(IV) isopropoxide and an aldehyde result either in a-hydroxyallenes without axial dissymmetry or in /J-hydroxyalkyn-es90 91. 

Jeong and co-workers utilized a cobalt-alkyne complex to enhance enantioselectivity of the addition of bis (homoallyl)zinc to propargyl aldehydes 68 by the exaggeration of steric environment. The reaction provided optically enriched propargyl alcohol 69 in the presence of a chiral ligand and titanium tetra(isopropoxide) in excess. Adduct 69 was subjected to PKR to yield optically enriched bicyclic compounds 70 (Equation (39)). ... 

DeCamp et al.t19l synthesized the lactone intermediate of the 1-hydroxyethylene isostere with high yields and stereoselectivity. As summarized in Scheme 10 (Section 10.6.2), the titanium homoenolate is prepared from ethyl 3-iodopropionate. The iodide is metalated with zinc/copper couple to give the iodozinc homoenolate species. The alkyltitanium homoenolate is then generated by transmetalation of the iodozinc precursor with one of the several chlorotitanium isopropoxide species. The resulting titanium homoenolate reacts with a N-protected a-amino aldehyde, leading to a mixture of 45-diastereomers. In the last step, the product is lactonized. 

Titanium(IV) isopropoxide, 311 a,(3-Epoxy aldehydes and ketones Fluorine-Acetonitrile, 135 Oxodiperoxymolybdenum-(pyridine)(hexamethylphosphoric triamide), 227 a,(3-Epoxy silanes Allyltriisopropylsilane, 11 m-Chloroperbenzoic acid, 76 Esters (see also Dicarbonyl compounds, Unsaturated esters)... 

It was noticed as early as 1925 that alkoxides of calcium, magnesium and particularly aluminum could catalyze the reduction of aldehydes by ethanol as shown in equation (65).242,243 Removal of very volatile acetaldehyde is easily achieved to drive the reaction to the right. In 1926, Ponndorf devised a method in which both aldehydes and ketones could be reduced to alcohols by adding excess alcohol and aluminum isopropoxide.244 Such reductions are today referred to as Meerwein-Ponndorf-Verley reactions. Although alkoxides of a number of metals, e.g. sodium, boron, tin, titanium and zirconium, have been used for these reactions, those of aluminum are by far the best. 

In contrast to titanium enolates of ketones, titanium enolates of aldehydes exhibit practically no stereoselectivity in aldol reactions. However, titanation of dimethylhy-drazones of aldehydes with 1 results in substrates (2) that show high eryt/iro-selecti v i ty in aldol-type reactions with aldehydes (equation I). Bromotitanium tris(diethylamide) can be used in place of 1, but is less efficient, as is Ti(IV) isopropoxide.6... 

A BINOL-salen ligand catalyses the enantioselective addition of TMSCN to aldehydes at room temperature, in the presence of titanium(IV) isopropoxide.269... 

Furukawa et al. [274] and Natta cl al. [275,276] succeeded independently in the preparation of crystalline polyacetaldehyde by using some organometallic compounds, such as diethylzinc or triethylaluminium, for the low-temperature polymerisation of acetaldehyde. Metal alkyls and metal alkoxides, e.g. aluminium isopropoxide, zinc ethoxide or ethyl orthotitanate, have also polymerised other aldehydes such as propionaldehyde and trichloroacetaldehyde to give crystalline polymers (Table 9.3) [270,275,277], A highly crystalline isotactic polymer has been obtained from the polymerisation of w-butyraldehyde with triethylaluminium or titanium tetrachloride-triethylaluminium (1 3) catalysts. Combinations of metal alkyl, e.g. diethylzinc, with water [278] or amine [279] appeared to give very efficient catalysts for aldehyde polymerisations. 

E)- or (Z)-l,3-Dienes. Lithiation (f-BuLi) of 1 followed by addition of 1 equiv. of titanium(lV) isopropoxide results in a reagent that reacts with aldehydes to form an intermediate p-oxidophosphine, which is not isolated, but is converted into a (Z)-1,3-diene by alkylation with methyl iodide (equation I). ... 

Enantioselective addition of (C2Hs)2Zn to RCHO. Of a variety of chiral N-sulfonylamino alcohols, 1 was found to be the most effective ligand for asymmetric addition of dicthylzinc to aldehydes catalyzed by titanium(IV) isopropoxide in methylene chloride. Addition of calcium hydride or 4 A molecular sieves docs not affect the enantioselectivity but can increase the yield. 

Tridentate BINOL catalysts can be derived from titanium tetra(isopropoxide), BINOL ligands, and hindered amine bases. These catalysts have also been shown to provide good yields and ee s for the aldol reactions at low temperatures of 2-methoxypropene with several aldehydes to the P-hydroxyketones, but an acid workup of the products is required. 

---