Methylenation isopropoxide

Aluminum isopropoxide has proved to be a very effective initiator for the polymerization of lactones pPL, 6VL, eCL, DXO, and pBL and dilactones D,L- and L-LA, and GA. It is worth noting that cycHc carbonates, e.g., 2,2-dimethyltri-methylene carbonate (DTC) and cycHc anhydrides such as adipic anhydride (AA) have also been polymerized by aluminum trialkoxides with the unique possibility to control the molecular parameters of the polycarbonate (PDTC) and polyanhydrides (PAA). This is illustrated in Scheme 2 and the preferred reaction conditions are given in Table 3. 

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

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

Insertion complexes of lanthanide isopropoxides with isocyanate can act as carbon dioxide carrier for the carboxylation of active methylene compounds , as exemplified in Scheme 25 [241], The catalytic formation of urethane is based on insertion of isocyanate into the La-OtBu bond of La3(OfBu)9(THF)2 [242]. 

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). 

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). ... 

In the course of our studies on organic and macromolecular syntheses with lanthanoid alkoxide, we have foimd that a lanthanoid complex, formed by the addition of a lanthanoid isopropoxide (LnlUPrla) to a heterocumulene bearing nitrogen atom (R-N=C=X isocyanates and carbodiimides), served as a novel COj carrier for the rapid carboxylation of active methylene compounds (Y-CHj-Z) under mild conditions such as room temperatxue and atmospheric pressure (Scheme 1). 

Carboxylation reaction of active methylene compounds with lanthanoid system was first attained by using a lanthanoid complex obtained from the reaction between lanthanum isopropoxide (LalO Prlj) and 2 equiv of phenyl isocyanate (Ph-N=C=0). Under CO2 at atmospheric pressure, phenylacetonitrile, an active methylene compound (equimolar with respect to LalCyPrlj), was effectively... 

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 dione adduct 25 (440 mg) and aluminum isopropoxide (1.83 g) were dissolved in dry isopropanol (8 mL). The mixture was boiled gently, and acetone and isopropanol were distilled slowly from the reaction mixture through a short column. From time to time isopropanol was added to maintain a constant volume. After one hour no more acetone could be detected in the distillate. The reaction mixture was then concentrated under reduced pressure, treated with ice-cold 2 N hydrochloric acid, and extracted with methylene chloride/ether (1 3). The organic phase was washed with sodium bicarbonate and saturated sodium chloride solution, and concentrated. The residue was crystallized twice from acetone/ether, to give 230 mg of colorless lactone 26. 

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. 

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... 

Al-isopropoxide followed by a soln. of excess diazomethane in methylene chloride added to a soln. of yohimbine in the same solvent, and the product isolated after 12 hrs. yohimbine methyl ether. Y 84%. F. e. s. A. Popelak and G. Lettenbauer, Arch. Pharm. 295, 427 (1962). 

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