Catalytic Enantioselective 1,2-Diboration of 1,3-Dienes: Versatile Reagents for Stereoselective Allylation
作者:Laura T. Kliman、Scott N. Mlynarski、Grace E. Ferris、James P. Morken
DOI:10.1002/anie.201105716
日期:2012.1.9
More with boron: The development of catalyticenantioselective 1,2‐diboration of 1,3‐dienes enables a new strategy for enantioselective carbonyl allylation reactions (see scheme). These reactions occur with outstanding levels of stereoselection and can be applied to both monosubstituted and 1,1‐disubstituted dienes. The carbonyl allylation reactions provide enantiomerically enriched functionalized
Convergent Synthesis of the Polyene Macrolide (-)-Roxaticin
作者:Scott D. Rychnovsky、Rebecca C. Hoye
DOI:10.1021/ja00084a017
日期:1994.3
ether followed by elaboration of the polyene using Wollenberg's method gave a tetraenal. The macrocyclic ring was closed using an intramolecular Horner-Emmons Wittig reaction, and acid-catalyzed deprotection completed the synthesis of roxaticin. Our synthesis of roxaticin illustrates a first generation approach to the highly convergent synthesis of polyenemacrolide antibiotics that should ultimately
Directed reduction of .beta.-hydroxy ketones employing tetramethylammonium triacetoxyborohydride
作者:D. A. Evans、K. T. Chapman、E. M. Carreira
DOI:10.1021/ja00219a035
日期:1988.5
The mild reducing agent tetramethylammonium triacetoxyborohydride reduces acyclic P-hydroxy ketones to their corresponding anti diols with high diastereoselectivity. a-Alkyl substitution does not significantly affect the stereoselectivity of these reductions. In all cases examined, good to excellent yields of diastereomerically homogeneous diols were obtained. The mechanism of these reductions involves
温和的还原剂四甲基铵三乙酰氧基硼氢化物以高非对映选择性将无环 P-羟基酮还原为其相应的反二醇。α-烷基取代不会显着影响这些还原的立体选择性。在所有检查的情况下,都获得了良好到极好的非对映异构体均质二醇的产率。这些还原的机制涉及三乙酰氧基硼氢化物阴离子将乙酸盐与底物醇进行酸促进的配体交换。所得氢化物中间体,大概是烷氧基二乙酰氧基硼氢化物,还原近端 OH 0 OH OH 0 Me,NHB(OAc), Mew Me&OR - OR Me he
Inter- and Intramolecular Differentiation of Enantiotopic Dioxane Acetals through Oxazaborolidinone-Mediated Enantioselective Ring-Cleavage Reaction: Kinetic Resolution of Racemic 1,3-Alkanediols and Asymmetric Desymmetrization of <i>M</i><i>eso</i>-1,3-polyols
Acetals derived from racemic 1,3-alkanediols undergo kinetic resolution in chiral oxazaborolidinone-mediated ring-cleavage reaction with nucleophiles such as enol silanes and allylic silanes. Enantioselectivity of the reaction is affected by nucleophiles, the N-sulfonyl groups of oxazaborolidinones, and the substituents attached to the acetal carbon. For disubstituted acetals rac-1 and for trisubstituted
Asymmetric Aldol Additions: Use of Titanium Tetrachloride and (−)-Sparteine for the Soft Enolization of <i>N-</i>Acyl Oxazolidinones, Oxazolidinethiones, and Thiazolidinethiones
作者:Michael T. Crimmins、Bryan W. King、Elie A. Tabet、Kleem Chaudhary
DOI:10.1021/jo001387r
日期:2001.2.1
N-methyl-2-pyrrolidinone, selectivities of 97:3 to > 99:1 were obtained for the Evans syn aldol products using N-propionyl oxazolidinones, oxazolidinethiones, and thiazolidinethiones. The non-Evans syn aldol adducts are available with the oxazolidinethione and thiazolidinethiones by altering the Lewisacid/aminebase ratios. The change in facial selectivity in the aldoladditions is proposed to be a result of