Methylenation titanium isopropoxide

Allyltriisopropoxytitanium, 213 Allyltris (diethy lamino) titanium, 216 /-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 jx-Chlorobis(cyclopentadienyl)-(dimethylaluminum)- p-methylene-titanium, 71... 

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). ... 

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). ... 

It is advantageous to utilize either titanium isopropoxide w trim l laluminum complexes widi aldehydes in general, because pinacol-coupled diols form with the Zn/CHsBis/TiQ systems as minor side products. No evidence of Simmons-Smith-type side products was observed with any of the methylenation reagents. Additional examples of the reaction with aldehydes are presented in Table 11. 

Diiodomethane-Zinc-Titanium(IV) isopropoxide, 115 Iodomethyltrimethylsilane, 315 Tributyl(iodomethyl)tin, 314 a-METHYLENE-y-BUTYROLACTONES (see Un-saturated Lactones)... 

A 2-L, three-necked, round-bottomed flask equipped with a mechanical stirrer with Teflon blades, thermometer, and nitrogen inlet is charged with 1.00 L of methylene chloride (Note 1) and 39.9 mL (38.1 g, 0.134 mol) of titanium(IV) isopropoxide (Note 2). The flask content is stirred and cooled under nitrogen in a dry ice-ethanol bath to -70°C. To the flask is then added 33.1 g (27.5 mL, 0.151 mol) of diethyl (2R,3R)-tartrate (Note 3) and 25.0 g (0.25 mol) of E-2-hexen-l-ol (Note 4). Asmall volume of methylene chloride is used to ensure complete transfer of each material to the reaction flask. To the flask is then added 184.5 mL (0.50 mol) of 2.71 N anhydrous tert-butyl hydroperoxide in toluene (Note 5) which has been precooled to -20°C (Note 6). The addition causes a temperature increase to -60°C the temperature of the reaction mixture is allowed to come to 0°C over a 2.0-hr period (Note 7). 

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. 

The reaction is normally performed at low temperatures (-30 to 0°) in methylene chloride, and is catalytic in the chiral component diethyl or diisopropyl tartrate (DET or DIPT), and in titanium tetra-isopropoxide, provided water is rigorously excluded 4 A molecular sieves may be added to ensure this. Both enantiomers of tartaric acid are commercially available, allowing the synthesis of either enantiomer of the epoxylalcohol. The key to the remarkable enzyme-like enantioselectivity lies in the complex formed from the... 

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