Allylic amination, palladium-mediated

Several examples of transition metal catalysis for the synthesis of piperidines appeared this year. Palladium catalyzed intramolecular urethane cyclization onto an unactivated allylic alcohol was described as the key step in the stereoselective synthesis of the azasugar 1-deoxymannojirimycin . A new synthetic entry into the 2-azabicyclo[3.3.1]nonane framework was accomplished through a palladium mediated intramolecular coupling of amine tethered vinyl halides and ketone enolates in moderate yields . A palladium catalyzed decarboxylative carbonylation of 5-vinyl... 

De Meijere and co-workers have extended the scope of this process by applying this palladium-mediated multicomponent reaction to the bicyclopropylidene 72 as the alkene partner (Scheme 8.33). In this case, the intermolecular trapping of 7r-allyl palladium intermediate 73 with a soft carbonucleophile or with primary or secondary amines affords only products 74 having a methylenecyclopropane end group [78],... 

Palladium-mediated intramolecular aminations onto an allylic alcohol <1998TL5971> or allene <1998TL5421> are reported for the synthesis of piperidines. An intermolecular version of the allene-based reactions has been reported in the synthesis of spiropiperidines (Equation 167) <1998JOC2154>. 

FIGURE 24 Generation of supramolecular catalysts for allylic amination (89) (A) assembly of pseudoenantiomeric bisoxazoline derivatives. CAChe-minimized model of the palladium-containing supramolecular complex and (B) palladium-mediated enan-tioselective allylic amination. (See Color Insert in the back of this book.)... 

Few examples of carboaminations of normal double and triple bonds are known. Similarly to allylic alcohols, tosylated allylic amines with (cthoxy)ethene form 2-ethoxy-4-vinylpyrrolidines 2. The reaction, mediated by stoichiometric amounts of palladium(II) acetate, can be changed to catalytic if copper(II) acetate is added as reoxidant of palladium(O). Moderate stereoselectivity (d.r. 64 36) is reported, however, without further structural assignment. 

A series of l-benzazepin-5-ones were furnished via a rhodium-catalyzed intermolecular hydroacylation of an allyl amine onto an aryl aldehyde (14AGE3688) while a one-step synthesis of a number of tetrahydro-3-benzazepines was achieved through the palladium-mediated reaction of phenylethylamines with allenes (14JOC9578). 

Most of these procedures are incompatible with common linkers, and are therefore unsuitable for the transformation of support-bound substrates into carboxylic acids. A more versatile approach for this purpose is the saponification of carboxylic esters. Saponifications with KOH or NaOH usually proceed smoothly on hydrophilic supports, such as Tentagel [19] or polyacrylamides, but not on cross-linked polystyrene. Esters linked to hydrophobic supports are more conveniently saponified with LiOH [45] or KOSiMe3 in THF or dioxane (Table 13.11). Alternatively, palladium(O)-mediated saponification of allyl esters [94] can be used to prepare acids on cross-linked polystyrene (Entries 9 and 10, Table 13.11). Fmoc-protected amines are not deprotected under these conditions [160],... 

DeShong (Scheme 20). Thus, reaction of nitrones with vinyl silanes followed by reduction provides Peterson - type intermediates which can then be eliminated to either Z- or E-products. Homoallylic amines were also prepared using allylsilane in the initial cycloaddition. Substitution reactions of allylic nitro compounds have received considerable attention and some examples are outlined in Scheme 21. In each case, examination of the regiochemistry of the reaction was of paramount concern, the results using palladium being superior to the SnCl mediated process. Allylic sulphides constitute yet another group of... 

The allylsulfonyl group, introduced by reaction with aUylsulfonyl chloride in the presence of a totiary amine, has been shown to be a useful new hydroxyl protecting group. While stable towards deacetyladon, desilylation, and acetal hydroly it is selectively removed under mild conditions by palladium (0)-mediated allyl transfer m morpholine. ... 

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