Imidate -sigmatropic rearrangement

O-Allyl imidate esters undergo [3,3]-sigmatropic rearrangements to /V-allyl amides. Trichloromethyl imidates can be made easily from allylic alcohols by reaction with trichloroacetonitrile. The rearrangement then provides trichloroacetamides of IV-allylamines.260... 

The reactions of 1,2,3-triazolium 1-imide (277) with a range of alkene and alkyne dipolarophiles give rise to a variety of new ring systems (Scheme 54). Compounds (276) and (278) are obtained from (277) by reaction with acrylonitrile and DMAD, respectively. These reactions are tandem 1,3-dipolar (endo) cycloadditions and sigmatropic rearrangements which are regio- and stereospecific <90JCS(Pl)2537>. Kinetic and mechanistic studies show that these reactions are dipole-HOMO controlled. The second-order rate constants are insensitive to solvent polarity, the reaction indicates... 

Besides commonly used TsN=IPh, TsNs can also be employed as a nitrene source. Bach and Korber have recently reported an Fe(iii)-catalyzed imidation of allyl sulfides 200 with iV-/ //-butyloxycarbonyl azide (BocNs), followed by [2,3]-sigmatropic rearrangement (Scheme 21). " The azide reacts with FeCl2 to generate Fe(iv) nitrene complex 201, which then reacts with allyl sulfide 200, to give an intermediate sulfimide 203, presumably through Fe(iii) intermediate 202. 

The synthesis of a new series of tetrahydro-oxazolo[4,5-d]-1,2,3-triazoles (102) has been reported. The triazolium imide 1,3-dipole (104) reacted with ( )-cinnamaldehyde in refluxing ethyl methyl ketone. It is significant that it was to the C=0 bond of the a,/ -unsaturated aldehyde that the cycloaddition took place, yet analogous addition to benzaldehyde or aliphatic ketones was not possible. The primary products of the cycloaddition reaction (105) underwent a sigmatropic rearrangement to furnish the new ring system (102) as shown in Scheme 23 <90JCS(P1)2527>. 

The 1,3-transposition of oxygen and nitrogen functions by [3.3] sigmatropic rearrangement has found extensive application in the synthesis of allylic amines or amides. These reactions can be classified as 3-aza-l-oxa-Cope or aza-Claisen rearrangements. They are thermodynamically favorable for the transformation of an imidate to an amide. 

It was already known that glucose could be converted into the cyclic ether 118 and a [3,3] sigmatropic rearrangement (Overman style, see chapter 19) on the allylic imidate ester 119 should give 120, a derivative of 117. The should has to be there because it is not possible to forecast the stereochemical outcome with certainty. 

Conversion of ailylic alcohols into rearranged allylic amines. This transposition can be accomplished by conversion of an allyhc alcohol, for example geraniol (1), into the trichloroacetimidate (2) by treatment with sodium or potassium hydride and then with trichloroacetonitrile (ether, -10° and then 20°). This allylic imidate undergoes a [3.3] sigmatropic rearrangement when... 

The thermal and acid-catalysed ring-contractions of l-acyl-l,2-diazepines to pyridine iV-imides and/or 2-(acylamino)pyridines is well known. Moore has now reported a new reaction path in the thermolysis of (84), leading to the 1,3-diazepine (85) in addition to a 6-benzamidopyridine. A stepwise conversion of (84) into (85) is favoured, assisted by electron release from oxygen, rather than a sigmatropic rearrangement " [cf. the formation of (65) described above]. 

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