Heck-carbonylation cascades

Scheme 3-39 Heck-carbonylation cascades [110a]. A = [PdCPPhjljClJ, 40 atm CO, NEtj, C HeMeCN/MeOH, 100°C, 24h. B = [PdCPPhjlJ, l.l atm CO, KEt3, THE, 60°C, 24h.

One pot cascade sequences involving a Stille coupling (Heck/Stille, Heck/ carbonylative Stille, Stille/Diels Alder, Stille/electrocyclization, etc.) have been reported in literature. ... 

In 2002, Aggarwal et al. developed an efficient route to unsaturated carboxylic acid 44 by a palladium-catalyzed Heck cyclization/carbonylation cascade of vinylic bromide 43 [18a] (Scheme 6.9). By choosing the appropriate phosphine ligand and intensive optimization, the formation of linear carboxylic acid 45 and the direct Heck-type product can be restricted. Recently, the same group applied this cascade transformation as the key step to the total synthesis of avenaciolide [18bJ. 

SCHEME 6.9 Palladium-catalyzed Heck cyclization/carbonylation cascade. 

SCHEME 6.10 Cascade Heck/carbonylation for substrates possessing P-hydrogens. 

Successive Heck reactions, including carbonylation steps, have been used in cascade reactions which allow the simultaneous formation of five or more C—C bonds.93... 

In principle, carbonylative cyclization, that is, acylpalladation or Ac—Pd process, or noncarbonylative cyclization, that is, sample carbopalladation or C—Pd process, in the presence of CO and a Pd catalyst. Various possibilities with halo alkenes as representative substrates are shown in Scheme 2P Those processes that incorporate CO in the cyclization processes are discussed in Part VI including Sects. VI.4-VI.6. hi this section, those cases that do not incorporate CO during the cychzation processes but do so only after cyclization will be discussed. Such cychc carbopalladation-carbonylative termination tandem and cascade processes are represented by the Type II C—Pd process in Scheme 2, which may take place in competition with the other processes shown in Scheme 2, especially the cyclic Heck reaction (Type 1 C—Pd process) and cyclic carbopalladation involving cyclopropa-nation (Type 111 C— Pd process). 

Recent advances in the cyclizations catalyzed by transition metals and their complexes are reviewed. The catalytic cyclizations discussed here include various carbocyclizations, for example, cycloisomerization, cycloaddition, reductive cyclization, and so on cascade carbocyclizations, for example, cyclotrimerization, silylcarbocyclization, and Heck reaction carbonylative carbocyclizations cyclohy-drocarbonylations intramolecular hydrosilylations intramolecular silylformyla-tions and aldol cyclizations. These reactions serve as efficient and useful methods for the syntheses of a variety of heterocycles and carbocycles that are important... 

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