Allylic trichloroacetimidate

Acid-catalyzed allylation with allyl trichloroacetimidate was used to protect the hydroxyl group without migration of any acyl group present in the molecule of saccharide [89]. Thus, methyl 3,4-di-O-allyl-2,6-di-0-benzoyl-oc-D-mannopyranoside was obtained from the corresponding dibenzoate in 68% yield using trifluromethane-sulfonic acid as a catalyst. 

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. 

Intramolecular substitutions offer a convenient and stereoselective method for the introduction of amino functionalities. A strategy for the preparation of vicinal m-hydroxy amino moieties entails the halocy-clisation of allylic trichloroacetimidates.77 Conversion of the hydroxyl of unsaturated sugar derivatives into a trichloroacetimidate, followed by Ar-bromosucciniinide (NBS) or JV-iodosuccinimide (NIS) mediated intramolecular cyclisation, gives bromo- and iodo-oxazoline derivatives (Scheme 3.13a). The oxazoline can be hydrolysed with mild acid to unmask the amino functionality, and the halogen can be removed by treatment with tributyltin hydride. 

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. 

Allylic trichloroacetimidates, generated in situ from cyclic y-hydroxy-a,P-unsaturated sulfones, undergo intramolecular conjugate addition to the vinyl sulfone moiety to afford oxazolines. Acid hydrolysis of the oxazolines generated... 

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. 

The regioselectivity of the reaction is strongly dependant, on the configuration of the double bond. When allylic trichloroacetimidates in which a terminal double bond were cyclized, the cyclization proceeded in a 5-exo mode directed by electronic factors (Table 8, entries 1-5)145 147. 

Finally, in order to directly incorporate the nitrogen and sulphur functionalities in a single step with total stereoselectivity, the chiral allylic trichloroacetimidate 16 was treated with methyl sulfenyl triflate to give the corresponding A -sulfenyl imidate 17 in good yield. Further reaction of 17 with methyl sulfenyl triflate gave the 4,5-dihydro-l,3-oxazole 18, together with a minor amount of the trichloroacetamide 19, formed by hydrolysis of 18246. 

Li, C, Fuchs, P L, Methanesulfenyl triflate promoted iminosulfenylation of an allylic trichloroacetimidate. An efficient and stereospecific total synthesis of (-I-) mannostatin A, Tetrahedron Lett., 35, 5121-5124, 1994. 

Regio- and stereo-controlled iodocyclizations of allylic trichloroacetimidates provide a route to cw-hydroxyamino sugar from hexenopyranosides. For example, conversion of the hydroxyl of compound 117 into the trichloroacetimidate 118 followed by IDCP-mediated intramolecular cyclization, gives iodo-oxazoline derivative 119, which is reduced (Bu3SnH) and hydrolyzed (pyridine, TsOH) to afford IV-acetyldaunosamine methyl glucoside 120 (O Scheme 57) [95]. 

The rearrangement of allyl trichloroacetimidate into allyl trichloroacetamide (Overman rearrangement) has been used for the synthesis of amino sugars. For example, the trichloroace-... 

For example, on heating at 160 °C in 1,2-dichlorobenzene, the allylic trichloroacetimidate 84 smoothly rearranges into the corresponding 2-amino-2-deoxy sugar 85 [81]. The suprafacial rearrangement from C2 to C4 is similarly performed to obtain the 4-amino-4-deoxy sugar derivative 87 [82] (O Scheme 15). 

In the recent total synthesis of sphingofungin E (90), Overman rearrangement of an allylic trichloroacetimidate derived from diacetone-D-glucose 91 generated tetra-substituted carbon... 

Anderson, C. E., Overman, L. E. Catalytic Asymmetric Rearrangement of Allylic Trichloroacetimidates. A Practical Method for Preparing Allylic Amines and Congeners of High Enantiomeric Purity. J. Am. Chem. Soc. 2003, 125, 12412-12413. 

Nagashima, H., Wakamatsu, H., Ozaki, N., Ishii, T., Watanabe, M., Tajima, T., Itoh, K. Transition metal catalyzed radical cyclization new preparative route to y-lactams from allylic alcohols via the [3.3]-sigmatropic rearrangement of allylic trichloroacetimidates and the subsequent ruthenium-catalyzed cyclization of N-allyltrichloroacetamides. J. Org. Chem. 1992, 57, 1682-1689. 

Thermal and mercury(ii)-catalysed [3,3]sigmatropic rearangement of allylic trichloroacetimidates and allylic pseudo-ureas" e.g. geraniol, linalool) are useful for the 1,3-transposition of hydroxy- and amino-groups the former is synthetically preferred. The [2,3]sigmatropic rearrangement of allylic sulphoxides has been used to effect an alkylative 1,3-carbonyl transposition of enones (e.g. carvone). ... 

Moreover, complete chirality transfer is found in the thermal rearrangement of optically active allyltrichloroacetimidates. By treatment with sodium hydride and trichloroacetonitrile, ( + )-( )-4-phenyl-3-buten-2-ol [( + )-3] is converted to ( + )-4 in 94% yield. When the allyl-trichloroacetimidate (+)-4 is heated in toluene under reflux the [3,3] shift product ( + )-5 is obtained in 74% yield with exclusively E geometry437. 

The total synthesis of (-l-)-lactacystin (1) has been achieved via Overman rearrangement of allylic trichloroacetimidate derived from D-glucose as an effective method for chiral synthesis of a,a-disubstituted amino acid derivatives (Schemes 1 and Selective... 

As a preliminary mechanistic proposal, we hypothesize that the palladimn(ll)-phosphoramidite catalyst acts as a chiral n-acid to activate the amine iV-oxide substrate (Scheme 1S.291. similar to the mechanism proposed for the Overman rearrangement of allylic trichloroacetimidates. While it is not clear whether the reactive species is oxide-bound complex 119a or olefin-bound complex 119b, we propose heterocycle 120 as an intermediate in this cyclization-induced mechanism Grob-type fragmentation eventually reveals O-allylhydroxylamine 117 and the palladium(n)-phosphoramidite catalyst, which can reenter the catalytic cycle. 

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