Claisen rearrangement imidate

The high catalytic activity also enabled aza-Claisen rearrangements to form Al-substituted quaternary stereocenters (Fig. 26) [71]. The catalyst does not need to distinguish between differently sized substituents on the double bond of 49 (e.g., R = CDa, R = CHs, ee = 96%), indicating that coordination of the olefin is the stereoselectivity predetermining step. The imidate-N-atom subsequently attacks intermediate 47-1 from the face remote to the Pd-center totally resulting in a... 

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... 

A. Claisen Rerrangements of Ketene Aminats and Imidates. A reaction that is related to the orthoester Claisen rearrangement utilizes an amide acetal, such as dimethylacetamide dimethyl acetal, in the exchange reaction with allylic alcohols.257 The products are y, 8-unsaturated amides. The stereochemistry of the reaction is analogous to the other variants of the Claisen rearrangement.258... 

Scheme 6.17 gives some examples of the orthoamide and imidate versions of the Claisen rearrangement. Entry 1 applied the reaction in the synthesis of a portion of the alkaloid tabersonine. The reaction in Entry 2 was used in an enantiospecific synthesis of pravastatin, one of a family of drugs used to lower cholesterol levels. The product from the reaction in Entry 3 was used in a synthesis of a portion of the antibiotic rampamycin. Entries 4 and 5 were used in the synthesis of polycyclic natural products. Note that the reaction in Entry 4 also leads to isomerization of the double bond into conjugation with the ester group. Entries 1 to 5 all involve cyclic reactants, and the concerted TS ensures that the substituent is introduced syn to the original hydroxy substituent. 

In 1975, van der Baan and Bickelhaupt reported the synthesis of imide 37 from pyridone 34 as an approach to the hetisine alkaloids, using an intramolecular alkylation as the key step (Scheme 1.3) [23]. Beginning with pyridone 34, alkylation with sodium hydride/allyl bromide followed by a thermal [3,3] Claisen rearrangement gave alkene 35. Next, formation of the bromohydrin with A -bi omosuccinimide and subsequent protection of the resulting alcohol as the tetrahydropyranyl (THP) ether produced bromide 36, which was then cyclized in an intramolecular fashion to give tricylic 37. 

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. 

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 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. 

Other leaving groups like the enantiomerically pure imidate85 (Table 8, entry 11) can also be used to give the substituted product with net retention of configuration. Without an external nucleophile, transition metal-catalyzed Claisen rearrangement occurs for allyl imidates. 

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. 

Y,S-Unsaturated anilides Et2NLi converts N-phenyl imidates to A-silyl ketene MO-acetals, which undergo Claisen rearrangement at room temperature. 

Claisen rearrangements of cyclic allyl imidates and thioimidates, and the cyclization (79) - (80). iV-Alkylations of (81) have also been reported, as has a study of the products of acid decomposition of iV-nitrosocaprolactam. ... 

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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