Heteroaromatics alkynylation

Alkenyl-, alkynyl-, aryl- and heteroaromatic-stablllzed llthlooxiranes... 

Flash-vacuum pyrolysis has been utilized to synthesize complex thiophene-containing polycyclic hydrocarbons from alkynyl-substituted thiophenes and chlorovinyl-substituted thiophenes <99TL2789>. For example, the bowl-shaped heteroaromatic thiophene 92 was prepared by flash-vacuum pyrolysis of benzotrithiophene 91 <99CC1859>. 

As noted for the Heck reaction, aryl, alkenyl, and alkynyl bromides, iodides, and triflates are best for the oxidative addition. However, aromatic, heteroaromatic, alkenyl, and even alkyl boronic acids and esters can be coupled effectively. The reaction appears almost oblivious to other functional groups present ... 

Various aryl, alkenyl and even alkylborane reagents of different reactivity can be used for coupling with aryl, alkenyl, alkynyl and some alkyl halides, offering very useful synthetic methods. The cross-coupling of aryl and heteroarylboronic acids with aryl and heterocyclic halides and triflates provide useful synthetic routes to various aromatic and heteroaromatic derivatives. Sometimes, the reaction proceeds in the... 

Fischer carbene complexes 639 can be coupled with 3-alkynyl-2-heteroaromatic carbaldehydes to form initially the alkenylcarbene complexes 640, which undergo CO insertion to give the ketene intermediates 641, which upon ring closure affords heteroaryl-fused 277-pyran-2-ones (Scheme 147) <2001TL777, 2002JOC4177>. 

FVP of alkynyl-substituted and chlorovinyl-substituted thiophenes 877 affords the corresponding naphtho[ ]thio-phenes 878 <1999TL2789>. The bowl-shaped heteroaromatic thiophene 880 is prepared from an isomeric mixture of 879 by the FVP method <1999CC1859>. 

UV studies suggest that in 1-vinyl-imidazoles and -benzimidazoles there is conjugation with the heteroaromatic ring. Certainly the reactivities of such compounds would indicate that they are not normal alkenes, nor are the alkynyl compounds typical of other alkynes. They are very prone to polymerization processes, and electrophilic addition reactions are often quite difficult to accomplish. When 1-styrylimidazoles are prepared, the trans compound is much more likely to eventuate as the more stable isomer 73CJC3765, 76JCS(PD545). 

As shown in O Table 2, this procedure enables the synthesis of a variety of 8-C-glucosides and -C-galactosides with substituents such as alkyl, allyl, vinyl, alkynyl, propargyl, aromatic, heteroaromatic [20], and acetyl groups. 

Allylation. Carbamates of 2-Allyl-l,2-dihydroquinoline and the isoquinoline analogs are formed by the catalyzed reaction of the heteroaromatic compounds with CICOOR and allyltrimethylsilane (also alkynylation ). Heterocyclization of isonitriles containing an allylsilane moiety, initiated by C-acylation, is promoted by AgOTf. ... 

The therapeutic potential of HENECA for the treatment of cardiovascular diseases, and the need for more selective A2a agonists prompted us to synthesize a number of new 2-alkynyl derivatives of NECA bearing hydroxyl, amino, chloro, cyano, and heterocyclic groups or substituted aromatic or heteroaromatic rings in the side chain [27,28]. 

A Stille-related paper reported different regioselectivities in a q clocarbo-palladation in which the multistep reaction described terminated in a Stille cross-coupling. Mechanistic studies with deuterium provided a background for a discussion of the different outcomes when alkynyl or vinyl stannanes were used. Microwave heating was found to increase the rate of the reaction with two vinyl stannanes and one heteroaromatic stannane as substrates [80]. 

Pyrrole derivatives have been used less frequently in the Diels-Alder reaction because this heteroaromatic compound is susceptible to electrophilic substitution. Thiophen and some of its derivatives react with alkynyl dienophiles under vigorous conditions to form benzene derivatives by extrusion of sulfur from the initially formed adduct. 

III.2.7 HETEROAROMATICS VIA PALLADIUM-CATALYZED CROSS-COUPLING 457 D.i.c. Alkynylation... 

As for alkynylation of heteroaromatic A-oxides, it has been reported that azine A-oxides react with lithium and/or potassium acetylenides to give the corresprMiding ethynylazines. It is worth noting that the reaction with lithium acetylenide requires a subsequent acylation of the intermediate anionic adduct for rearomatizatiOTi, whereas in case of potassium acetylenide, the aMto-aromatization takes place (Scheme 35) [73],... 

G. P. Jana, S. Mukherjee, B. K. Ghorai, Synthesis 2010, 3179-3187. Multicomponent approach for the synthesis of phenanthridine and acridine ring systems via the coupling of Fischer carbene complexes with heteroaromatic o-alkynyl carbonyl derivatives. 

Scheme4.31 Rhodium-catalyzed addition of arylboronic adds to alkynyl nitrogen heteroaromatic compounds.

Lautens, M. Yoshida, M. Rhodium-catalyzed addition of arylhoronic acids to alkynyl aza-heteroaromatic compounds in water. J. Org. Chem. 2003, 68,762—769. 

Application of Pd-catalyzed cross-coupling to a-alkynylation, a-alkenylation, and a-arylationt of heteroaromatic a,/3-unsaturated carbonyl derivatives, such as 5-iodouracil derivatives, has been known since the early 1980s (Scheme 50). Although these reactions are formally related to the Pd-catalyzed a-substitution discussed herein, the robust aromatic nature of the heteroaromatic substrates makes the requirements for their a-substitution less demanding. These reactions should therefore be viewed as a class of CTOss-coupling reactions involving aryl hahdes rather than a-halo-a,/3-unsaturated carbonyl compounds. In most... 

An efficient Cu-catalyzed cycloisomerization of alkynyl imines into the 2-monosubstituted and 2,5-disubstituted pyrroles was reported by Gevorgyan and coworkers (Scheme 8.3). This methodology was efficient to the synthesis of various types of fused heteroaromatic compounds and even synthesis of ( ) monomorine. A C(sp )-H of the substrate was activated during this copper-catalyzed pyrrole formation [12]. Moreover, they also realized the... 

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