Benzoyl group regioselective benzoylation

It has been proven that palladium catalyzed reductive Heck reactions are versatile and high-yield approach for preparing of new bioactive alkaloid epibatidine (1) analognes fromN-benzoylated 2-aza-bicyclo[2.2.1]hept-5-ene (3) and it has been shown that in case of aryl- groups reaction progresses regioselectively. All Heck type reactions proceed exo-selectively, leading to the same stereochemistry as fonnd in 1. 

The regioselective attack of nonactivated C-H-bonds by an excited carbonyl group is demonstrated with the transannular cyclization of bicyclic diketones 76, which can easily be prepared from cyclic ketones 75 according to Stetter et al. [61]. Upon irradiation, the selectively excited benzoyl... 

A stereoselective synthesis of (+)-pilocarpine (7) starting from L-histidine (2) has been worked out by Noordam et al. (88 - 90). Use was made of the S configuration of the amino acid, which is the same as that of C-3 of the lactone ring in both (+)-pilocarpine and (+)-isopilocarpine. Furthermore, regioselective N-alkylation reactions of the imidazole nucleus of histidine had been developed by Beyerman et al. (29,91). Schemes 3 and 4 depict the different ways of the regioselective alkylations. For the synthesis of pilocarpine, the N7I-methylation has been performed via Nb-protection with the 4-nitrobenzenesulfonyl group, instead of the benzoyl group (29). 

CEt=CPh-0) are prepared from the regioselective coupling of the coordinated alkyne with an acetyl or benzoyl group in the reactions of Tp NbMe(OMe)(PhC=CR) and Tp NbPh(OMe)(PhC=CEt) with... 

The enantioselective synthesis (51) of the side chain 30 of taxol had been achieved by way of stereospecific Sharpless epoxidation of cij-cinnamyl alcohol (29a), giving 29b (see Scheme 6). Following oxidation of the alcohol group, protection of the resulting carboxylic acid, regioselective opening of the epoxide with azide, benzoylation, and reduction, a suitably substituted moiety (28) was available which, after protection and deprotection of the acid function to form 30, was coupled to baccatin III. 

The methyl group at position 6 is more reactive for radical bromination than the 2-methyl group of 2,6-dimethylquinazolin-4 3//)-one ° or 2,6-dimethyl-4-methylsulfanylquinazo-line. Regioselective bromination with N-bromosuccininiide (NBS) or 1,3-dibromo-5,5-dimethylhydantoin (DDH) using benzoyl peroxide as a catalyst gives the respective benzyl bromides in good yields. 

In our syntheses of Salmonella structures [10,13,19,21], the heptose derivative 1 was used as a precursor for all of the heptose residues found in the target molecules. An acceptor precursor for later formation of the (1 —> 7)-linkage was obtained by regioselective silylation of the primary hydroxyl group followed by benzoylation of OH-6 (Scheme 3). Van Boom et al. postpone the oxidation step... 

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