Alkynylating reagents

The alkynyl reagent 9 was recently introduced for the dia stereoselective synthesis of tertiary propargylic alcohols144. 9 can be prepared as a solid 1 1 complex with tetrahydrofuran by treatment of 9-methoxy-9-borabicyclo[3.3.1]nonane with (trimethylsilylethynyl)lithium, followed by addition of boron trifluoride-diethyl ether complex. The nucleophilic addition of reagent 9 to (R)-2-methoxy-2-methylhexanal (10) afforded a mixture of the diastereomers 11 with a considerable preference to the nonchelation-controlled (3S,4R)-isomer144. 

Allylic phosphonate esters react with imines, in the presence of a palladium catalyst, to give P-lactams. " Alkynyl reagents such as BuC=CO Li react with imines to form P-lactams. 

The addition of anionic heteroatom-centered nucleophiles (HO, MeO, pyr-azolate, etc.) and carbanions (CN , enolates, aUcyl or alkynyl reagents) to the cationic allenylidenes [Ru( 7 -C9H7)(=C=C=CR R )(PPh3)2][PF6] [125-128,... 

Alkynyl(phenyl)iodonium salts have attracted a significant interest as stable and readily available powerful alkynylating reagents. The preparation, structure, and chemistry of alkynyliodonium salts was extensively covered in a recent review [4]. 

The ability of alkynyl groups to bridge two metals may be employed in the construction of heterometallic complexes in a controlled manner (Figure 4.20 Chapter 6). Many metals will react directly with terminal alkynes or acetylide salts under basic conditions however, use is often made of copper alkynyls as tr /i.v-alkynylating reagents [usually generated in situ with catalytic amounts of Cu(I) salts]. 

Lodaya, J.S.. and Koser. G.E. Alkynyliodonium salts as alkynylating reagents. Direct conversion of alkynylphenyliodoniiun tosylates to dialkyl alkynylphosphonates with trialkyl phosphites, J. Org. Chem., 55. 1513. 1990. 

Zhang, J.-L., and Chen, Z.-C., Hypervalent iodine in synthesis. Part 25. Alkynylphenyliodonium tosylates as alkynylating reagents. Direct conversion of alkynylphenyhodonium tosylates to dialkyl alkynylphosphonates with sodium dialkylphosphonates, Synth. Commun., 28, 175, 1998. 

Another attractive TOP sequence involves use of a combination of the Bestmann-Ohira reagent and Mn02. In these examples, a range of activated alcohols are oxidized to the corresponding aldehydes, which in turn are efficiently trapped by the subsequently added alkynylating reagent (eq 103). 

Polymer-supported alkynyliodonium tosylates 34 can be prepared by treatment of reagent 4 with terminal alkynes in the presence of p-toluenesulfonic acid (Scheme 5.20) [57]. Polymers 34 are effective alkynylating reagents toward sodium sulfinates and benzotriazole [57]. 

Scheme 9.39 Alkynylborinates 109 and 111 as efficient alkynylation reagents in Suzuki-Miyaura cross-couplings [300, 302].

R groups other than simple alkyls may be introduced by using aryl, alkenyl, or alkynyl reagents. 

Because of the high reactivity of the hypervalent bond, hypervalent iodine reagents have been intensively used in organic chemistry [10-15]. They occupy a central place among electrophilic alkynylation reagents as they are ideally suited... 

With the discovery and use of alkynyliodonium salts, a new class of electrophilic alkynylation reagents has emerged. Because of their impressive reactivity, they could be broadly used to introduce acetylenes on carbon nucleophiles, heteroatoms, or metals. Nevertheless, with the exceptions of the alkynylation of nitrogen and new applications in the synthesis of alkynyl-metal complexes, most research on alkynyliodonium salts has been concentrated in the years 1985-1995, with rare more recent breakthroughs. In particular, very few applications using modem catalytic methods have appeared, in stark contrast to the use of aryhodonium salts in arylation reactions [99]. One of the possible reasons for this drying out of the field is the relatively low stability of alkynyliodonium salts, which often makes their use challenging. 

The chemistry of alkynyl-metal complexes has been reviewed recently.Glassical synthetic routes to half-sandwich alkynyl-ruthenium and alkynyl-osmium complexes of general composition [M(G=GR)(77 -G7,Ht )(L )(L )] are based on the reactions of appropriate halide precursors with lithium/sodium alkynyl reagents or... 

This synthetic protocol, although not widely applicable to various transition metals, provides a convenient route for the preparation of metal alkynyl complexes without the use of Cu(i) catalyst or strongly basic alkynylating reagents (Scheme 10.8). This metal-free method not only opens up the possibility of using a wider range of alkynyl ligands in the preparation of metal alkynyls but also eliminates possible -coordination of the catalyst to the alkynyl units. 

In the case of formation of the rhenium(I) complex 69 (Scheme 38), the alkynyl reagent [I(C=CSiMe3)Ph][OTf] has been used to add an additional alkyne functionality to convert a diyne to a triyne. ... 

---