Rearrangement of allylic imidates

Caller M, Hollis TK, Overman LE, Ziller J, Zipp GG (1997) First enantioselective catalyst for the rearrangement of allylic imidates to allylic amides. J Org Chem 62 1449-1456... 

Donde Y, Overman LE (1999) High enantioselection in the rearrangement of allylic imidates with ferrocenyl oxazoline catalysts. J Am Chem Soc 121 2933-2934... 

Kang J, Yew KH, Kim TH, Choi DH (2002) Preparation of bis [palladacycles] and application to asymmetric aza-Claisen rearrangement of allylic imidates. Tetrahedron Lett 43 9509-9512... 

Kang J, Kim TH, Yew KH, Lee WK (2003) The effect of face-blocking in the enantiose-lective aza-Claisen rearrangement of allylic imidates. Tetrahedron Asymmetry 14 415 18... 

The asymmetric aza-Claisen rearrangement of allyl imidates, (86) (87), has been shown to be catalysed by homochiral cationic palladium(II) complexes, and a series of enantiopure cyclopalladated ferrocenyl amines and imines have been... 

Bis(oxazoline) ligands have also been employed in the catalytic enantioselective aza-Claisen rearrangement of allylic imidates, " chirality recognition in the determination of the ee of l,l -bi-2-naphthol, " and the enantioselective formation of double and triple helicates. 

In a complementary approach, Larry Overman of the University of California at Irvine, has developed (J. Org. Chem. 2004,69,8101) a Co catalyst that effects the rearrangement of allylic imidates such as 9 with high . There is no need for the starting allylic alcohols to be perfectly trans, as imidates from cis allylic alcohols do not participate in the rearrangement. 

Claisen rearrangement of ally l imidates.1 This Pd(II) catalyst effects exclusive [3, 3] rearrangement of allylic imidates at 25° to allylic amides. Rearrangement of the chiral (E)-allylic imidate 1 results in a mixture of two chiral allyl amides 2 and 3. Thermal rearrangement of 1 results only in 2. 

The palladium(II)-catalyzed rearrangement of allyl imidates for the formation of allyl amines has also been investigated for chiral imidates (Eq. (6)) [12], The chiral imidate 15 undergoes a palladium(II)-catalyzed rearrangement to 16, which was applied for the synthesis of (/ )-N-(trichloracetyl)norleucinol 17 as presented in Eq. (6). 

The proposed catalytic cycle35 involves the formation of a six-membered cyclic carbenium ion intermediate D with n-bonded metal. The failure of rearrangement of allylic imidates with a methyl group at the olefinic 2-position is presumably due to the difficulty of forming a tertiary carbon-metal bond (Table 4. entry 5)59. The stereocontrol of the metal-catalyzed rearrangement is different from the thermal one because of er-bonding of palladium or mercury in the transition slate. 

Rearrangement of Allylic Imidates. Overman and co-workers reported an interesting application of this chiral diamine to induce enantioselectivity in Pd(II)-catalyzed rearrangement of allylic imidates to allylic amides (eq 5). 

Donde, Y., Overman, L. E. High Enantioselection in the Rearrangement of Allylic Imidates with Ferrocenyl Oxazoline Catalysts. J. Am. Chem. Soc. 1999, 121, 2933-2934. 

Heterocyclic analogues of BINAP, such a< 2,2, 5,5 -tetramethyl-4,4 -bis(dipheny Iphosph and tested in the Heck reaction. Incorporaut sulfinyl group to a double bond elicits enj intramolecular Heck reaction. Optically ai ides are produced from (/ )-l-f-butylsulfinylcy Palladacycle (109) and its analogues ind rearrangement of allylic imidates. - For a thioamides, it is convenient to allylate thi dine. This process involves a thio-Claisen n Enantioselective deprotonation of ketones slum bis[yV-benzyl-N-(a-phenethyl)]amide.-- tonation of enolates. ... 

Palladacycle (109) and its analogues induce chirality of A -allylalkanamides during rearrangement of allylic imidates. For a synthesis of a-branched chiral 4-alkene-thioamides, it is convenient to allylate thioamides of (-F)-frany-2,5-diphenylpyrroli-dine. This process involves a thio-Claisen rearrangement. 

The catalysed rearrangement of allylic imidates including allylic trichloroace-timidates such as (12.12) has been reported by Overman using palladium catalysts with some of the highest ees obtained using the cobalt oxazoline palladacycle (12.13). 

Overman and co-workers carried out extensive studies on Pd(II)-catalyzed asymmetric allylic rearrangement of allylic imidates to form enantioenriched allylic amides. They achieved 97 % ee as the best result by the reaction of the allylic imidate 612 using the cyclopalladated ferrocenyl oxazoline 613 having elements of planar chirality as a catalyst precursor, and discussed the mechanism of the reaction [220]. 

Table 8.1 Rearrangement of allylic imidate catalyzed by the palladacycle catalysts/AgOOCCFj in CH2H2...

The size of the oxazoline substituent in the catalysts (8.30-8.32) was increased to 3-methoxy-3-pentyl (8.32), and an iodide-bridged dimer was activated in CH2CI2 by deiodination with Ag(OOCCF3). These in iitw-generated species catalyzed the rearrangement of -allylic imidate to allylic amide with moderate to good yields with enantioselectivities of 72-79 % ee (Nos. 8-10). 

A chiral TRIP anion combined with a palladacycle provides an active catalyst for enantioselective rearrangement of allylic imidates to the corresponding amide products (Scheme 98). Although the catalyst contains a chiral palladacycle, the stereoselectivity is induced by the chiral phosphate anion (Scheme 98). 

T. K. Hollis and L. E. Overman, /. Organomet. Chem., 1999, 576, 290-299. Palladium Catalyzed Enantioselective Rearrangement of Allylic Imidates to Allylic Amides. 

Palladium Catalyzed Enantioselective Rearrangement of Allylic Imidates to Allylic Amides. 

Aza-Claisen rearrangement of allylic imidates and thiocyanates in presence of o-xylene under microwave irradiation resulted in corresponding amides and isothiocyanates (Gonda et al., 2007). The reaction rate was enhanced 8-30 and 24-80 times, respectively. 

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