Metal mediated, acylation

Photolysis of [(Z)-2-(acyloxy)ethenyl]carbene complexes (= 4-acyloxy-1-chroma-l,3-dienes) (CO)sCr=C(OEt)-CH=C(OCOR1)R (Z)-169 (R = C6H5, t-Bu, c-Pr R1 = C6H5, c-Pr, c-C7H7CH2, f-Bu, Me2C=CH) with UV light of >300 nm affords 2-butene 1,4-diones R CO —C(OEt)=CH — COR (E)-170 (60-68%) by a novel metal-mediated acyl migration. Compounds (Z)-171 and furans 172 are formed as minor products (Scheme 72).4g... 

Transition-metal-mediated alkylation, aryiation, and acylation... 

To expand the diversity of their libraries Brill et al.16 also modified various heterocycles by alkylation, acylation, or metal-mediated coupling reaction prior to resin capture. A remaining chloro substituent was still available for nucleophilic displacement or a palladium-mediated coupling reaction with anilines, phenols, and boronic acids on solid phase [see Fig. 10 for the preparation of purine derivative (62)]. 

Angew. Chem. Int. Ed. Engl. 44, 3668-3688, 2005 Kent, M. and Tepe, J.J., One-pot Friedel-Crafts/ Robinson-Gabriel synthesis of oxazoles using oxazolone templates, J. Org. Chem. 70, 4211 213, 2005 Movassaghi, M. and Ondrus, A.E., Enantioselective total synthesis of tricyclic myrmicarin alkaloids, Org. Lett. 7, 4423 426, 2005 Paizs, C., Katona, A., and Retey, J., The interaction of heteroaryl-acrylates and alanines with phenylalanine ammonia-lyase form parsley. Chemistry 12, 2739-2744, 2006. Cuprous ions have been observed to promote a Friedel-Crafts acylation reaction (Kozikowski, A.P. and Ames, A., Copper(l) promoted acylation reactions. A transition metal-mediated version of the Friedel-Crafts reaction, J. Am. Chem. Soc. 102, 860-862, 1980). 

Imines are reduced by triethylsilane to their amines when the proper Ir orNi catalysts areemployed. Non-metal-mediated reductions of C=N groups by EtsSiH are also possible. Among these, the trifluorosulfonic acid promoted reductive amidation of aliphatic and aromatic aldehydes with EtsSiH is an excellent way to mono (V-alkylate aliphatic and aromatic amides, thioamides, carbamates, and ureas (eq 26). It is also worth noting that trifluorosulfonic acid/EtsSiH reduces acyl- and tosylhydrazones to hydrazines and 2-aminopyrimidines to 2-amino-dihydro-or 2-aminotetrahydropyrimidines (eq 27). ... 

Synthesis of amides from the coupling reactions of esters and amines is a potentially attractive method however, stoichiometric amounts of promoters or metal mediators are normally required [52], Complex 8 also catalyzes the amide synthesis from esters and amines and the reaction is general and efficient, and proceeds under neutral conditions, thus providing an environmentally benign method [15]. As demonstrated in the alcohol acylation process (Section 1.3.3, Table 1.6), when symmetrical esters are used, acylation of amines occurs by both acyl and alkoxo parts of the esters and they are incorporated in the products, and the only byproduct generated from this reaction is H2. 

Martinez and coworkers investigated the Dbtz benzannulation reaction in the synthesis of 2,3-disubstituted-l, 4-naphthoquinones. This represents the first focused investigation on the use of this interesting transition metal-mediated carbene-based reaction for the synthesis of a small combinatorial library of these target molecules. The authors initially explored the attachment of the Fischer carbene complex to the resin in a smooth four-step protocol. Reaction of an aryllithium species with Cr(CO)g generated the metallated intermediate. Subsequent reaction with A-tetrabutylammonium bromide (TBAB) furnished the required ionic complex, which was 0-acylated and attached to the Wang resin (Scheme 8.8). 

Aliphatic nitriles react slowly with phenols and phenyl ethers in the presence of trifluoromethanesulphonic acid to give ketones after hydrolysis, in a variation of the Houben-Hoesch reaction. The crystalline complex of copper(i) triflate and benzene induces the acylation of aromatic substrates with selenol esters, affording a transition-metal mediated version of the Friedel-Crafts reaction. Aromatic carboxylic acids can be converted into symmetrical diaryl ketones in good yield by treatment of their 5-(2-pyridyl)thioesters with bis-(l,5-cyclo-octadiene)nickel [equation (15)]. In contrast to other methods for preparing symmetrical aromatic ketones, this method allows their preparation from a single starting material. 

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