Rearrangement trichloroacetimidate

Synthesh of amines by l3,3]sigmatropie rearrangement Trichloroacetimidic esters (2) of allylic alcohols (1) can be prepared in 80-100% yield (crude) by reaction with trichloroacetonitrile catal3rzed by the corresponding sodium or potassium alkoxide (O, ether). Inverse addition is preferred for secondary or tertiary alcohols. These esters undergo Claisen-type rearrangement at 25-140° to give allylic trichloroacetamides (3), in which the rrans-isomcr usually predominates. 

Nomura H, Richards CJ (2007) An investigation into the allylic imidate rearrangement of trichloroacetimidates catalyzed by cobalt oxazoline palladacycles. Chem Eur J 13 10216-10224... 

By spontaneous sigmatropic rearrangement of the glycal 3-trichloroacetimidate made with NaH, CI3CCN,... 

Allyl imidate esters undergo [3,3] sigmatropic rearrangements to A -allyl amides. Trichloroacetimidates can be easily made from allylic alcohols by reaction with trichloroacetonitrile. The rearrangement then provides trichloroacetamides of iV-allyl-amines.176 177... 

Besides oxygen, other nucleophiles have also been successfully employed as acceptors. For instance, N-, C-, S-, and / -glycosyl derivatives have been obtained from corresponding nucleophiles and O-glycosyl trichloroacetimidates in the presence of acid catalysts [1 ]. For instance, aryl-C-glycosjdes have been recently synthesized from phenols in an efficient Fries-type rearrangement reaction [37]. 

The attempted Pd(II)-catalysed aza-Claisen rearrangement of the trichloroacetimidate (145) yielded the diastereoisomerically pure cyclopropane derivative (146) (Scheme 55).275... 

Rearrangement of the acetate of the optically active cyanhydrin 463 proceeds stereoselectively to yield the oc,/ -unsaturated nitrile 464 with 89% ee [197]. Allyl trichloroacetimidate 465 is rearranged from O to N to give 466 at room temperature with retention of the stereochemistry [198]. 

The Overman Rearrangement allows the conversion of readily available allylic alcohols into allylic amines by a two-step synthesis involving the rearrangement of an allylic trichloroacetimidate to an allylic trichloroacetamide with clean 1,3-transposition of the alkenyl moiety. 

Very recently Sutherland and coworkers merged the Pd-catalyzed Overman rearrangement with RCM and ATRC (Fig. 44) [256]. Treatment of dienols 179 with trichloroacetonitrile in the presence of 10 mol% Pd(MeCN)2Cl2 afforded the non-isolated trichloroacetimidate 180, which underwent the [3,3] rearrangement to /V-dienyltrichloroacetamides 174. They were immediately subjected to the RCM/ ATRC sequence using 10 mol% of 145. When chiral cobalt complex (S)- or (R)-181 was used as the catalyst for the Overman rearrangement, indolinones 177 were isolated in 51-70% yields and 89-94% ee. 

The Overman rearrangement, a thermal [3,3]-sigmatropic rearrangement of allylic trichloroacetimidates, is an attractive procedure for the preparation of ally] amines from allyl alcohols (Eq. (4)) [7]. 

The first step in this reaction is formation of the allyl trichloroacetimide 8 formed from allyl alcohol 3 by reaction with trichloroacetonitrile. The allyl amides 9 are formed by the [3,3]-sigmatropic rearrangement of 8, followed by hydrolysis. The reaction proceeds with good yield for primary and secondary amides however, for products where the amide nitrogen is bound to a tertiary carbon atom the yields are generally low. 

L. E. Overman, Thermal and mercuric ion catalyzed [3,3]-sigmatropic rearrangement of allylic trichloroacetimidates. 1,3-Transposition of alcohol and amine functions,. /. Am. Chem. Soc., 96 (1974) 597-599. 

Hetero-Claisen rearrangement. The rearrangement of allylic trichloroacetimidates (8.35) to allylic trichloroacetamides (8.36) is an example of the hetero-Claisen rearrangement ... 

The thermal rearrangement of O-allyl trichloroacetimidates 1 affords the corresponding 7V-allyl amides 31 2, which have been cyclized with the aim of obtaining amino diols or amino alcohols different to those from the cyclization of the trichloroacetimidates. Cyclization of these latter substrates 1 leads to 4,5-dihydro-4-(l-iodoalkyl)oxazoles 2, while treatment of unsaturated trichloroacetamides 3 with /V-iodosuccinimide3 in chloroform affords the corresponding 4,5-dihydro-5-(l-iodoalkyl)oxazoles 4 in high yield. These heterocyclic products are protected forms of the corresponding amino alcohols. 

In the synthesis of ( + )-polyoxamic acid36, representing a common structural feature of the polyoxin-type antifungal antibiotics, rearrangement of a trichloroacetimidate 1, derived from L-tartrate, gives a 1 1 mixture of diastereomers 2 and 3, showing no induction by the stereogenic centers outside the electrocyclic arena. 

Low 1,2-diastereoselection is also found in the thermal rearrangement of trichloroacetimidates derived from chiral <5-amino allylic alcohols54 55, which is contrary to the results of the palladium-catalyzed rearrangement (see Section 7.6.1.2.). 

Rearrangement of the trichloroacetimidate of the racemic bicyclic allylic alcohol 6 provided, exclusively, the labile e.vo-trichloroacetamide 7 shown in 52% overall yield52. 

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