Steglich rearrangement reaction

Scheme 10.8 Acetyl migration in a Steglich rearrangement reaction.

This reaction is related to the Steglich Rearrangement for benzofuran and indole derivatives. 

Reactions that exploit the nucleophilicity of NHC without involving a Breslow intermediate (101) are often encountered in the literature. For instance, a series of chiral NHCs has been evaluated for their catalytic ability to promote the Steglich rearrangement of oxazolyl carbonates (133) to C-carboxyazalactones (134) (Scheme 1) This NHC-catalysed version, involving azolium species (135) as non-Breslow intermediate, has been realized with only moderate levels of enantioselectivities. 

In 1998, Ruble and Fu [10] reported on the use of ferrocene-derived chiral 4-aminopyridines [11] in the Steglich rearrangement of 2-aryl-4-alkyloxazolones (Scheme 40.3). After the systematic optimization of several reaction parameters, the authors found that the planar-chiral ferrocene derivative (S)-l catalyzed the rearrangement of an array of 0-benzyloxycarbonyl azlactones with total... 

On this topic, several outstanding contributions were reported by Fu and coworkers,in which new asymmetric nucleophilic catalysts based on chiral ferrocene-type heterocycles were designed. To this end the planar-chiral PPY ferrocene complex (PPY = 4-(pyrrolidino)-pyridine (3.61) was prepared and resolved. Complex 3.61 catalysed the enantioselective rearrangement of A-acylated Azlactones to give C-acylated isomers with high yields and ee of 82-90%. The powerful effect of the chiral ferrocene scaffold was clearly evident if compared to the same reaction with the organic catalyst DMAP reported in 1970 by Steglich and Hofle where only racemic compounds were formed (Scheme 3.26). 

Sandmeyer synthesis (isatin) 145 Schmidt-Druey synthesis (pyridazine) 461 Schollkopf synthesis (oxazole) 173 Sharpless-Katsuki epoxidation 24 Shaw synthesis (pyrimidine) 468 Skraup-Doebner-Miller synthesis (quinoline) 400 Smiles rearrangement 446 Sommelet-Hauser rearrangement 136 Staudinger reaction 53 Steglich reagent (DMAP) 348 Stork isoxazole annelation 191... 

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