Influence des interactions de torsion dans les reactions d'addition sur les cyclohexanones. interpretation generale du deroulement sterique des reactions des hydrures ou des organomagnesiens sur les cyclohexanones

Improvements in oligodeoxyribonucleotide synthesis: methyl N,N-dialkylphosphoramidite dimer units for solid support phosphite methodology

“…The intermediate 2 and the final products 3e,f were characterized by their proton NMR spectra. Condensation of 3e with S'-O-dimethoxytrityl monomer phosphoramidite unit (4a) in the presence of tetrazole resulted in the formation of the completely protected phosphite dimer unit (8) in 74% yield (Scheme II). The presence of the phosphite linkage in 8 was confirmed by its 31P NMR spectrum showing resonance at -140.97 ppm, whereas its proton NMR spectrum (Experimental Section) showed signals at 0.07, 0.89, 3.53, and 3.78 ppm, indicating the presence of t-BDMSi, P-OCH3, and DMTr groups, respectively.…”

“…Found: C, 59.35; H, 5.62; N, 10.27; P, 2.72. 7V®-Benzoyl-5'-0-dimethoxytrityl-2'-deoxyadenosyl)-(3'--5 ')-P -methoxyphosphino-7V4-anisoyl-3'-O-(tert -butyldimethylsilyl)-2'-deoxycytidine (8). 3'-0-[(A/iV-Dimethylaminolmethoxyphosphinoj-A^-benzoyl-S'-CMdimethoxytrityl)-2'-deoxyadenosine (4a, 0.34 g, 0.45 mmol) and N4-anisoyl-3'-0-(tert-butyldimethylsilyl)-2'-deoxycytidine (3e, 0.14 g, 0.3 mmol) were dissolved in anhydrous acetonitrile (10 mL) and cooled in an ice bath, and a solution of tetrazole (0.063 g, 0.9 mmol) in acetonitrile (5 mL) was added dropwise.…”

Synthesis and characterisation of nematic liquid crystals containing atrans‐decalin ring

“…Further reduction of 2-decalone (4a, 4b) with NaBH 4 or LiAlH 4 stereoselectively gave mainly the alcohol with equatorial arrangement, according to the 1 H NMR spectra analysis. However, using LiAlH 4 reductive reagent gave a much higher stereoselectivity (over 90%) in the reduction of decalone, whereas lower stereoselectivity (below 75%) was obtained when NaBH 4 was used (27)(28)(29). Thus, LiAlH 4 was used in the reduction of the decalone and the ratios of equatorial:axial configurations of trans-6-alkyldecalin-2-ol and cis-6-alkyldecalin-2-ol in 5a and 5b were found be 91:9 and 90:10, respectively.…”

The Palladium-Catalyzed Enyne Cycloisomerization Reaction in a General Approach to the Asymmetric Syntheses of the Picrotoxane Sesquiterpenes. Part I. First-Generation Total Synthesis of Corianin and Formal Syntheses of Picrotoxinin and Picrotin

“…The addition of an acetaldehyde enolate equivalent must occur axially to create the third contiguous asymmetric center. While torsional strain should favor such a stereochemical outcome, steric strain should favor equatorial attack . Minimizing steric strain requires use of a sterically nondemanding nucleophile.…”