Steric Effects on the Titanium Tetrachloride Promoted Dimepization of Silyl Ketene Acetals

Generation of 1,2-Bisketenes from Cyclobutene-1,2-diones by Flash Photolysis and Ring Closure Kinetics1a

“…The cyclobutenediones except for 1g , o are known compounds. − , The bis( t -Bu) derivative 1g was made by two independent routes, as shown in eqs 2 and 3. The route of eq 3 from meso -2,3-di- tert -butylsuccinic acid ( 6 ) presumably involved the bisketene 2g as an intermediate. Evidence for the formation of 2g was obtained by the reaction of 7 with DMAP at room temperature, which gave spectral evidence for the presence of 10% of 2g together with the known 3a anhydride 8 (eq 4).…”

“…Dimethyl d , l -2,3-Di- tert -butylsuccinate ( dl -10). 13b Dione 1g (52.0 mg, 0.268 mmol) in 0.5 mL of CDCl 3 and 50 μL of MeOH was irradiated for 12 h at 6 °C with 350 nm light. The solvent was evaporated, leaving d , l - 10 (69.2 mg, 0.268 mmol, 100%) as the sole product: 1 H NMR (CDCl 3 ) δ 1.02 (s, 18), 2.50 (s, 2), 3.63 (s, 6); 13 C NMR (CDCl 3 ) δ 28.0, 34.3, 51.1, 54.0, 174.2; IR (CDCl 3 ) 1733 (vs), 1721 (vs) cm -1 ; EIMS m/z 227 (M + − MeO, 14), 145 (90), 131 (58), 113 (65), 57 ( t -Bu + , 100).…”

Stereo- and enantioselective polymerization of hexa-1,5-diene on heterogeneous Ziegler-Natta catalysts obtained with the use of optically active internal donors

“…[22][23][24][25][26] The best diastereomer ratio (rac and meso ) in the product, which is equal to 89 : 11, is achieved by treat ment of isopentanoic acid enolate with iodine. 26 Since in all other cases 21-25 the content of the rac form of 2,3 di isopropylsuccinate is no more than 70%, this procedure 26 was applied to synthesize the pure racemate of DIPS.…”

“…To increase the yield, we used the procedure of successive silylation of enolate of L menthyl isopentanoate with dimethyldichlorosilane to isolate product 5, which was further oxidized with titani um tetrachloride in CH 2 Cl 2 at 0 °С. 25 Di L menthyl 2,3 diisopropylsuccinate was prepared as a mixture of iso mers 6а, 6b, and 6с in the ratio of 1 : 2 : 5. We succeded in a threefold increasing the yield of pure di L menthyl (-) 2,3 diisopropylsuccinate 6с, which was isolated by crystallization, up to 20%.…”

“…A white sol id residue of the acid was then used without additional puri fication. 25 589 +18.20 (c 1, CHCl 3 ). Preparation of a heterogeneous catalyst (general procedure).…”