Carbopalladation enamides

Another common use of carbopalladation is to effect a net annelation by side chain installation followed by cyclization. One example from the synthesis of a protected form of the 2-quinolone portion of streptonigrin 40 begins with iodide 37 (Scheme Heck reaction of this electron-rich fully substituted aryl iodide 37 with methyl acrylate provides the substimtion product 38. Extended reflux of 38 under acidic conditions promotes double deprotection, isomerization, and cyclization reaction yielding enamide 39. Another example from the synthesis of ( )-aurantioclavine 41 involves coupling of aryl bromide Standard Heck conditions provide the substitution product 43 in excellent yield at the appropriate oxidation state for cyclization to form the azepine ring en route to the natural product... 

The nature of the alkene is important in determining reactivity. Indeed, electron-rich alkenes such as enamides, enoenamides, and alkenyl ethers are notably more reactive to carbopalladation. 

The aryl (or alkyl) palladium species needed for a Heck reaction can be generated fi om boronic acids and their derivatives if the overall reaction is conducted under oxidative conditions. In contrast to haloarenes, transmetalation is leaving the metal oxidation state unchanged. Therefore, an additional oxidant is needed to gain back Pd(ll) after a completed catalytic circle. So-called oxidative Heck reactions have been reported for the first time by Cho and Uemura and Karami et al The group of Park has shown that enamides are suitable substrates for this carbopalladation mode (Scheme 5-40). ... 

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