Epoxide-opening process

S. Y. Tosaki, R. Tsuji, T. Ohshima, M. Shibasaki, Dynamic ligand exchange of the lanthanide complex leading to structural and functional transformation One-pot sequential catalytic asymmetric epoxidation-regioselective epoxide-opening process, J. Am. Chem. Soc. 127 (2005) 2147. 

A stereoselective approach to tetrasubstituted (Z)-/3-hydroxy-o -TMS (trimethylsi-lyl)enol ethers occurs via a sequential addition/[ 1,2]-Brook rearrangement/epoxide-opening process of TMS-substituted oxiranyl anions with acylsilanes (Scheme 46). ... 

Scheme 13.37 One-pot sequential catalytic asymmetric epoxicdation-regioselective epoxide-opening process.

The same year, Shibasaki et al. showed that asymmetric epoxidation of ot,p-unsaturated amides by chiral lanthanide catalysts could he efficiently combined with a subsequent palladium-catalysed epoxide opening process in one-pot to give the corresponding p-aiyl a-hydroty amides in excellent... 

Nemoto T, Kakei H, Gnanadesikan V, Tosaki S, Ohshima T, Shibasaki M. Catalytic asymmetric epoxidation of ,(3-unsaturated amides efficient s5mthesis of p-aryl a-hydroxy amides using a one-pot tandem catalytic asymmetric epoxidation-Pd-catalyzed epoxide opening process. J. Am. Chem. Soc. 2002 124(49) 14544-14545. 

A major limitation of this method is the low pH at which the reactions are performed, which resulted in substantially lower yields in reactions with substrate progenitors of acid-sensitive epoxides, in which competing ring-opening processes effectively reduced the usefulness of the method. As an example, the oxidation of styrene had proceeded with 70% conversion after 3 h at 70 °C, but the observed yield of styrene oxide was only 2% (Table 6.5, Entry 5). 

Catalytic turn-over [59,60] in McMurry couplings [61], Nozaki-Hiyama reactions [62,63], and pinacol couplings [64,65] has been reported by Fiirst-ner and by Hirao by in situ silylation of titanium, chromium and vanadium oxo species with McaSiCl. In the epoxide-opening reactions, protonation can be employed for mediating catalytic turn-over instead of silylation because the intermediate radicals are stable toward protic conditions. The amount of Cp2TiCl needed for achieving isolated yields similar to the stoichiometric process can be reduced to 1-10 mol% by using 2,4,6-collidine hydrochloride or 2,6-lutidine hydrochloride as the acid and Zn or Mn dust as the reduc-tant (Scheme 9) [66,67]. 

The following is an example for a sequential one-pot epoxide formation/nucleophilic opening process using (S)-4-(benzyloxy)-l,2-butanediol, iV-(p-tohienesulfonyl)-imida-zole, and 2-lithio-l,3-dithiane ... 

An epoxide or oxirane group can react with nucleophiles in a ring-opening process. The reaction can take place with primary amines, sulfhydryls, or hydroxyl groups to create secondary... 

Porath, 1974). B/s-oxirane compounds also can be used to introduce epoxide groups into soluble dextran polymers in much the same manner (Boldicke et al., 1988 Bocher et al., 1992). The epoxide group reacts with nucleophiles in a ring-opening process to form a stable covalent linkage. The reaction can take place with primary amines, sulfhydryls, or hydroxyl groups to create secondary amine, thioether, or ether bonds, respectively (Chapter 2, Section 1.7). 

These processes have also been carried out through epoxide openings that occur with complete... 

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