Alkynes unactivated

Unactivated aziridines, such as 24, are not as reactive as their N-sulfonyl analogues. Nevertheless, in aqueous conditions they react with different nucleophiles, as Scheme 12.23 illustrates. Treatment with buffered azide at 50 °C gave 25 in 90% yield. Hydrazine proved potent even at room temperature and 26 was fonned in 95 % yield, while phenyltetrazole required heating at reflux in water. The resulting amines participated in dipolar cycloadditions with alkynes and condensations with P-diketones. 

Allenes and ketenes react with activated aikenes and alkynes. Ketenes give 1,2 addition, even with conjugated dienes.Ketenes also add to unactivated aikenes if sufficiently long reaction times are used. Allenes and ketenes also add to each other. 

Intramolecular cycloadditions between cyclobutadiene and an oxygen-tethered unactivated alkene (alkyne) offers an attractive route to benzo[c]furans (Scheme 26, <96JA9196>). 

Hydration of unactivated alkynes is an important method for functionalizing this plentiful hydrocarbon source. Therefore, a variety of metal ions have been proposed as catalysts for this reaction, and almost all of the reported additions of water to terminal alkynes follow the Markonikov rule. The hydration of l-aUcynes with Hg(II) salts in sulfuric acid [85], RuCh/aq.HCl [86, 87], K[Ru (edta-H)Cl] 2H20 [88], RhCl,.3H20/aq. HCl [89], RhCl3/NR4 [90], Zeise-type Pt(II) complexes [91-93], and NaAuCl4 [94] produced exclusively methyl ketones (Eq. 6.46). 

In aqueous media, the addition of unactivated alkynes to unactivated alkenes to form Alder-ene products has been realized by using a ruthenium catalyst (Eq. 3.44).180 A polar medium (DMF H20 = 1 1) favors the reaction and benefits the selectivity. The reaction was proposed to proceed via a ruthenacycle intermediate. 

A tremendous amount of progress has been made over the past decade in the understanding of the catalyzed reductive coupling of unactivated alkenes and alkynes. Both early and late transition metal complexes accomplish the reaction with good yields and with low catalyst loadings. Enynes and dienes can... 

Gold as an efficient catalyst has widely been used in furan synthesis. One example is shown below, in which the double hydroarylation of unactivated alkyne using 2-methylfuran afforded a difuranylmethane derivative in a moderate yield <06EJOC4340>. 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

In this context, alkynes have been investigated under carbometallation conditions in order to generate tri- or tetrasubstituted alkenes with very good stereochemical control.46 For the unactivated triple bonds, the major issue is the regioselectivity of the reaction. 

Organolithium reagents47 instead of organoaluminum derivatives48, 9 have been used for the carbometallation of unactivated alkynes under iron catalysis (Scheme 9). Thus, variously substituted alkynes 30 and 32, bearing a tertiary... 

We initially observed an addition reaction of tertiary phosphines to unactivated alkynes. The method was then applied to reactive alkenes, allenes and 1,3-dienes, and finally to unactivated alkenes (Scheme 4). Such a step-up methodology turned out to be effective in this study. 

The cross-coupling reaction of unactivated allenes and 1-alkynes has been efficiently achieved by making use of catalysis with HRh(CO)(PPh3)3 and Et3P, giving endo-(E)-enynes in high yields and selectivities (Scheme 16.95) [101],... 

Phenylacetonitriles can be induced to undergo Michael reactions with unactivated alkenes. For example, propenylarenes, formed in situ from allylarenes, react with phenylacetonitriles to form 3-aryl-l-cyano-2-methyl-l-phenylpropanes (70-98%) [3] by a procedure analogous to 6.4.1.B, Similarly, the nitriles react with alkynes giving allyl cyanides (80-95%) [38]. 

Broene RD (2007) Reductive Coupling of Unactivated Alkenes and Alkynes. 279 209-248 BrogginiM (2008) Nemorubicin. 283 191-206... 

Reductive cyclization onto an unactivated alkene or alkyne is also catalysed by chloro(pyridine)cobaloxine(ni). These reactions have been carried out in a divided... 

Rhodium catalysis has played a critical role in the development of this type of reaction. The rhodium-mediated [4 + 2] carbocyclization between dienes and unactivated olefins or alkynes is a notable early example of this concept [2]. Further investigations demonstrated the extension of this methodology to the reaction between a diene and an allene [3]. Expansion of the scope of this strategy, to both the intra- and intermolecular [5-1-2] homologs of the Diels-Alder reaction, was accomplished with a vinylcyclopropane and either an alkyne or an olefin to afford the carbocyclization adducts (Scheme 11.1) [4, 5]. 

Indeed, in a study of reaction rate and efficiency as a function of geminal substitution of the VCP, it was found that heteroatom substitution was not required to activate the VCP for intermolecular [5+2] cydoaddition (Tab. 13.14) [51]. Substitution for -H at the 1-position of the cyclopropane with -Me, -TMS, or - Pr led to an acceleration of the reaction that correlated with size of the substituent. Significantly, good to excellent yields and high, if not complete, regioselectivities are observed with a variety of mono-substituted alkynes and simple, unactivated VCPs. 

---