Copper-catalyzed alkynylation-cyclization

SCHEME 2.84 Copper-catalyzed intramolecular cyclization of alkynyl alcohols [124],... 

The palladium/copper-catalyzed coupling reaction of 2-iodo-3-methoxy-6-methylpyridine and terminal alkynes leads to the formation of o-methoxyalkynylpyridines which undergo electrophilic cyclization reactions to afford furo[3,2-3]pyridines in moderate yields <2005JOC10292>. A similar Pd/Cu-catalyzed reaction with hydroxypyridines and trimethylsilyl (TMS)-acetylene leads to the formation of alkynyl pyridines which cyclize to form furo[2,3- ]-pyridines in good yields <1998JME1357>. 

P-carbohnes [29] (Schane 3, equation 1). A variety of secondary amines were employed, and the method was adapted to the preparation of pyrrolo[3,2-/lindoles and dipyrrolo[3,2-h 2, 3 -c]pyridines [30]. Cacchi and colleagues synthesized 3-aroylindoles from the copper-catalyzed cyclization of lV-(2-iodoaryl)enaminones (equation 2) [31]. The latter were prepared from 2-haloanilines and a,p-ynones, which can react directly with 2-iodoaniline under the copper protocol to give 3-benzoyl-2-phenylindole (76%), thus bypassing the enaminone. Patel described a copper-catalyzed 3-aroylindole synthesis from 2-alkynylated... 

In this vein, alkynyl-functionalized (hetero)arenes were utilized in Pd-catalyzed arylation and cyclization events to reach tetrasubstituted alkenes. This strategy proved successful with an iV-phenylpropiolamide (Scheme 18a) [240] and N-(2-alkynylbenzyl)indoles (Scheme 18b) [241]. Copper catalysis was also viable, as demonstrated in reactions with 2-ethynyl anilides to yield benzoxazines (Scheme 18c) [242]. A copper-catalyzed carboarylation of electron-rich alkynes... 

The copper-catalyzed reaction of j8-styrylboronic acid with sodium azide afforded ( )-j8-styryl azide in good yield. In rare cases, the rearrangement of butatrienylidene and alkynyl complexes of iridium led to special enazides. A single example of the formation of an alkenyl azide via palladium-catalyzed cyclization of an allenic substrate has also been reported. ... 

Alkenylpyrimidines can undergo a copper(l)-catalyzed isomerization and cyclization on to an adjacent ring nitrogen as demonstrated by the synthesis of 6-propylpyrrolo[l,2- 7]pyrimidine 580 from the 2-alkynyl precursor 579 <2001JA2074>. A similar procedure with 2,4-dipropynylpyrimidine resulted in the formation of a bispyrrolopyrimi-... 

Cascade migration of acyloxy and phosphatyloxy group/cyclization reaction of alkynyl ketones catalyzed by copper or silver provided trisubstituted furans in high yields. A study of the reaction mechanism was also reported <07JA9868>... 

In a similar way, iminoalkynes containing aryl, alkenyl, and alkyl substituents undergoes Cul-catalyzed cyclization in excellent yields and short reaction times to give isoquinolines, pyridines, and pyrroles via a cycloisomerization (eq 18)4 Copper chloride is preferred, however, for the conversion of cyclic alkynyl imines to pyrrole-containing heterocycles. Copper iodide catalyzes the formation of furans from alkynyl ketones. ... 

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