Formation of Carboxylic Acids, Esters, and Amides

Aromatic and a, jS-unsaturated carboxylic acids and esters are prepared from aryl and alkenyl halides. 

Carbonylation of reactive iodides proceeds using PdCl2(PPh3)2 as a standard catalyst under mild conditions in the presence of a base. Several modified catalyst systems have been reported. For example, ligandless Pd charcoal is an active catalyst at 140 °C [1]. Uozumi reported that the amphiphilic phosphine-Pd complex (Pd-PEP) bound to PEG-PS resin is a very active and useful catalyst. Carbonylation 

Alkenyl halides and trifiates are easily carbonylated. Carbonylation of a-iodo enone 3 proceeded at 60 °C using Pd(OAc)2 and DPPP, and the ester 4 was obtained in 62% yield [6]. The lactam 5 was converted to the vinyl trifiate 6, which was carbonylated to afford the a, -unsaturated ester 7 [7], Carbonylation of the alkenyl iodide 8, possessing a labile peroxy group proceeded smoothly to give the a, -unsaturated ester 9 under 1 atm of CO at 60 °C in DMF. The peroxy group remained intact [8]. 

Alkenyl iodides can be generated in situ by hydroalumination of alkynes, followed by iodination, and a,jS-unsaturated esters are prepared by carbonylation without isolation of the iodide. As an example, the propargylic alcohol 10 was aluminated regio- and stereoselectively and converted to the alkenyl iodide 11. The intramolecular carbonylation of 11 afforded the dibutenolide 12 in 81 % yield. The reaction is a key step in the total synthesis of (-l-)-parviflorin [9]. 

Carbonylation is widely utilized for preparation of complex molecules of natural products. As one example, Leighton constructed the fully elaborated tetracyclic 

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