Sonogashira coupling cyclization

Some early examples involving microwave-assisted solvent-free Sonogashira couplings using palladium powder doped on alumina/potassium fluoride as catalyst were described by Kabalka and coworkers (Scheme 4.4) [150], In addition, this novel catalytic system has been used in microwave-assisted solvent-free Sonogashira coupling-cyclization of ortho-iodophenol with terminal alkynes, and similarly of ortho-ethynylphenols with aromatic iodides, to generate 2-substituted benzo[b]furans... 

Scheme 7.126 Solvent-free Sonogashira coupling-cyclization.

Scheme 53 Butenolides by sequential Sonogashira coupling-cyclization [110]...

Scheme 55 Polyunsaturated y-alkylidene butenolides by sequential Sonogashira coupling-cyclization [111] (newly formed bonds drawn in bold lines)...

A highly efficient synthesis of l-alkylidene-l,3-dihydrobenzo[f]furans from t>-hydroxymethyl iodoarenes and propargyl alcohols uses a bimetallic Pd/Cu-catalyzed Sonogashira coupling/cyclization reaction (Equation 132) <1999SL456>. Pd/l,4-bis(diphenylphosphino)butane (DPPB)-catalyzed reaction of t>-allylphenols under a CO atmosphere leads to carbonylative cyclization to form benzannulated lactones <2006ASC1855>. A similar carbonylative cyclization leads to the stereoselective formation of 3-alkenyl phthalides <2006T4563>. 

The microwave-assisted solvent-free Sonogashira coupling-cyclization of 0-iodophenols 4 with terminal alkynes 5 and that of o-ethynylphenols 6 with organic iodides 7 to generate 2-substituted benzo[h]furans (8 and 9) has been... 

Sonogashira coupling/cyclization [33], Manabe and indolization to give an assortment of 2,4-disubstituted... 

Scheme 19 One-pot syntheses of substituted chlorobenzo[b]furan derivatives via the ortho-selective Sonogashira coupling-cyclization sequence...

Scheme 12.18 Consecutive amine propargylation-Sonogashira coupling-cyclization synthesis of benzofuran 27 and indole 28.

Many cascade reactions, including the reaction between X—H and alkyne, have been reported. A Sonogashira coupling-cyclization cascade (e.g.. Scheme 19.66) is an especially good combination for heterocycle synthesis from haloarenes bearing a nucleophilic functionality at the 2-position. In this section, a quite limited number of useful cascade reactions, especially those including the latest frontiers of modern organic chemistry, are presented. 

SCHEME 635 Alkyne insertion/Sonogashira coupling/cyclization cascade. 

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