Alkynylation alkynylmetals

SCHEME 7. Pd-catalyzed alkynylation with alkynylmetals containing Zn, and Sn... 

TABLE 5. Natural products synthesized since 1996 by using the Pd-catalyzed alkynylation of alkenyl electrophiles with alkynylmetals containing Zn or Mg... 

For reviews of the Pd-catalyzed alkynylation with preformed alkynylmetals, see ... 

Alkynylation of aldehydes.3 The reaction of alkynylmetals with chiral aldehydes shows no or slight diastereoselectivity, but in the presence of TiCl4, alkyn-yltributyltin reagents react with the steroid aldehyde 1 with about 9 1 diastereoselectivity. TiCl4-catalyzed reaction of 1 with allyltrimethylsilane or allyltributyltin also shows similar and comparable diastereoselectivity. 

Alkynylmetal reagents, in i/>-hydridized carbon polymerization, 11, 673 Alkynyl(methoxy)borates, preparation, 9, 212 Alkynyl oligosilanes, preparation, 3, 433 Alkynylsilanes... 

Negishi and co-workers also reported in 1978 Pd-catalyzed alkynylation reactions with alkynylmetals containing Mg, B, A1 and Sn. But B and Sn versions have sometimes been known as the Suzuki and Stille alkynylation reactions, respectively. Negishi and co-workers during 1977-1978 reported the Pd-catalyzed alkynylation reactions of alkynylzinc reagents with 1-halo-l-alkynes and aryl halides. 

One characteristic feature of the MPV alkynylation is the chemoselective transfer of functionalized alkynyl groups to aldehyde carbonyls. Reaction of chloral with functionalized A1 reagent 28 in CH2CI2 proceeds nicely at room temperature to furnish alcohol 29 in good yield, leaving the keto functionality intact (Sch. 13) [34]. Such transformation is not easily realized by use of ordinary alkynylation procedures because of the difficulty of generating functionalized alkynylmetal reagents. 

Palladium-catalyzed cross-coupling involving alkynylmetals and related alkynyl nucleophiles alkynyl-aryl, alkynyl-alkenyl, and alkynyl-alkynyl coupling... 

Negishi, E.-i., Xu, C. Palladium-catalyzed alkynylation with alkynylmetals and alkynyl electrophiles. Handbook of Organopalladlum Chemistry for Organic Synthesis 2002, 1, 531-549. 

III.2.8.2 Palladium-Catalyzed Alkynylation with Alkynylmetals and Alkynyl Electrophiles... 

A.ii. Sonogashira Alkyne Synthesis versus Pd-Catalyzed Alkynylation with Preformed Alkynylmetals... 

Since Pd-catalyzed alkynylation with prefonned alkynylmetals is generally somewhat more involved than the Sonogashira alkynylation, the use of the former protocol has to be duly justified. The following differences between the two protocols are worth noting. 

B.iii. Scope of Pd-Catalyzed Alkynylation with Alkynylmetals Containing Mg and Zn with Respect to the Alkynyl Groups and Organic Electrophiles... 

III.2.8.2 PALLADIUM-CATALYZED ALKYNYLATION WITH ALKYNYLMETALS 539 TABLE 2. (Continued)... 

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