Internal acetylenes

Potassium 3-aniinopropylaniide [56038-00-7] (KAPA), KNHCH2CH2CH2-NH2, pX = 35, can be prepared by the reaction of 1,3-diaminopropane and potassium metal or potassium hydride [7693-26-7] (57—59). KAPA powder has been known to explode during storage under nitrogen in a drybox, and is therefore made in situ. KAPA is extremely effective in converting an internal acetylene or aHene group to a terminal acetylene (60) (see Acetylene-DERIVED chemicals). 

The reaction with internal acetylenes leads to a mixture of both regioisomers and stereoisomers.141... 

Going to extremes, the reactivity of internal acetylenic triple bonds compared with terminal olefinic double bonds was also checked. Diallyl ethers of commercial 2-butyne-l,4-diol and 3-hexyne-2,5-diol are available in high yield by phase transfer etherification. They are reacted under essentially the same conditions as those described in section 3.1, with the double bond now being in 100 percent excess at the beginning (Eq. 4). 

Recently, Kumada et al. (49) have published a report on what they refer to as dehydrogenative, stereoselective cis double silylation of internal acetylenes. This appears to be a variation of Eq. (53), with diethyl bipyridyl nickel(11) as the catalyst, in which hydrogen is liberated instead of being added to an alkene to form a saturated product. 

This interaction can be performed with the involvement of internal acetylenes, which was exemplified by the reaction of MeC=CC02Me with nitronate (164) (382) (Scheme 3.132, Eq. 3). This reaction is also regioselective, but the yield of the target aziridine is low. Nitronate (Me02C)2C=N0(0Me) also reacts with acetylenes (382). The carboxyl group in isolable N -alkoxyaziridines can be selectively reduced (Scheme 3.132, Eq. 4). 

In 1987, Yamanaka s group described a Pd-catalyzed reaction of halothiazoles with terminal acetylenes [51]. While the yield for the Sonogashira reaction of 2-bromo-4-phenylthiazole (89) with phenylacetylene to afford 90 was moderate (36% after desilylation), the coupling of 4-bromothiazole and 5-bromo-4-methylthiazole with phenylacetylene gave the desired internal acetylenes 91 and 92 in 71% and 65% yield, respectively. 

In 1987, Yamanaka s group described the Pd-catalyzed reactions of halothiazoles with terminal acetylenes [22a]. Submission of 4-bromo- and 5-bromo-4-methyloxazoles to the Sonogashira reaction conditions with phenylacetylene led to the expected internal acetylenes. 

A Ag/Pd-cathode hydrogenates 2-butyne-1,4-diol and acetylene dicarboxylic acid exclusively to the cis-olefin [323]. Similar results were obtained at a Cu net covered with spongy silver [324]. With dimethyl butynedioate the cis/trans ratio of the product dimethyl butenedioate on a Pd black cathode decreased with increasing pH both in electrolytic and catalytic hydrogenation [325]. On the other side at a Hg cathode a trans addition to alkynes occurs [326]. In methy-lamine/liCl, dialkylacetylenes are reduced to trans-olefins. Nonconjugated aromatic internal acetylenes are selectively reduced to aromatic trans-olefins [327]. 

The isomerization of secondary and tertiary a-acetylenic alcohols to a,(3-unsaturated carbonyl compounds via 1,3-shift. When the acetylenic group is terminal, the products are aldehydes, whereas the internal acetylenes give ketones. 

Synthesis of internal acetylenes from vinylic tellurides... 

Treatment of vinylic tellurides prepared by photopromoted carbotelluration of terminal acetylenes (see Section 3.16.3) with aqueous NaOCl, followed by pyrolysis, affords internal acetylenes in good yields. ... 

Another hydride, magnesium hydride prepared in situ from lithium aluminum hydride and diethylmagnesium, reduced terminal alkynes to 1-alkenes in 78-98% yields in the presence of cuprous iodide or cuprous r rt-butoxide, and 2-hexyne to pure cij-2-hexene in 80-81% yields [///]. Reduction of alkynes by lithium aluminum hydride in the presence of transition metals gave alkenes with small amounts of alkanes. Internal acetylenes were reduced predominantly but not exclusively to cis alkenes [377,378]. 

However, several years later Priester and coworkers revised the interpretation of the IR spectra of polylithiated acetylenes in terms of propargylide and allenic anions (Table 11) ". They divided the compounds into two categories those that can directly form lithioacetyUdes (the terminal acetylenes) and those that must undergo hydrogen or alkyl shifts to form acetylides (the internal acetylenes). 

While the mono- and dianions of internal acetylenes stiU have allenic structures, polylithiation of terminal acetylenes results in anions having a different structure, as previously reported (Scheme 9). 

Successive lithiation of propyne vs. allene and internal acetylenes RCH2C = C —R (-2200 cm )... 

Other examples of exo-dig-dmg closure are summarized in Table 8. Alkynes 152, 154, and 156 give 153, 155, and 157, respectively, as the sole product of CO incorporation. Both terminal and internal acetylenes undergo the cyclization to give (Z)-exo-dig-products. 

The application of immobilized heterobimetallic cobalt-rhodium in nanoparticles has also been reported. In the presence of water, CO, and amine, internal acetylenes 119 were converted to 3,4-disubstituted furan-2(5H)-ones 120 and 121 in high yields, in which an amine was necessary for the formation of furanone and a higher CO pressure was required for good yield (Equation (8)). It is important to notice that the catalyst has been easily recovered without loss of activity or formation of hydrogenated side-products. The reaction proceeded in good yield for the symmetric substrates (entries 1 and 2) while it always gave two regioisomers for asymmetric alkyne substrates (entries 3-8). The isomer ratio was dependent on the steric and electronic nature of the substituents. 

This carbenoid undergoes a Fritsch-Buttenberg-Wiechell rearrangement84 when warmed at room temperature, to give the internal acetylene derivative (equation 58)85. 

Tamao, K., Miyake, N., Kiso, Y., and Kumada, M., J. Am. Chem. Soc. 97, 5603 (1975) (A novel dehydrogenative cis double silylation of internal acetylenes with hydrosilanes catalysed by Et2Ni. bipy). 

The analogous palladium catalyzed reaction of internal acetylenes, 2-iodophenol and carbon monoxide leads to the selective formation of coumarins. The heterocyclic analogues of o-iodophenol are also effective. The o-iodopyridone shown in 4.16. for example gave rise to the formation of azacoumarin in 70% yield.18 In these processes the insertion of the acetylene derivative occurs in advance of the insertion of CO. Interestingly, the change of the acetylene to an alkene reverses the insertion order and leads to flavone formation.19... 

Terminal acetylenes and Ru3(CO)j2 yield complexes of the type [57] (9,190, 336), whereas internal acetylenes form either complexes [56] or acetylene-substituted RU4 complexes (229). Alternatively, two acetylene moieties are incorporated with formation of metallacyclopentadienes (229), a class of compounds more familiar in osmium cluster chemistry (cf. Chapter 3.4.). Instead of two acetylene molecules, one molecule of an arylbutadiene may be the precursor of the metallacycle (382). 

The same reagents may be used to conduct monohydroboration of internal acetylenes as well. Unsymmetrically disubstituted compounds usually produce a... 

Alkynes are more reactive in hydroalumination than alkenes. Hence, unlike internal alkenes, internal acetylenes readily undergo hydroalumination. Side reactions, however, may occur. Proton-aluminum exchange in terminal alkynes, for instance, leads to substituted products, and geminal dialuminum derivatives are formed as a result of double hydroalumination. In addition, nonsymmetric alkynes usually give mixtures of regioisomers. Appropriate reaction conditions, however, allow selective hydroalumination. Thus, the addition of isoBu2AlH to alkynes is a... 

B-Bromo and B-iodo-9-borabicyclo[3.3.1]nonane add similarly in a cis fashion to terminal triple bonds 471 They do not react, however, with alkenes and internal acetylenic bonds. In contrast to the results mentioned above, phenyl-substituted chloroboranes (PhBCl2, Ph2BCl) do not participate in haloboration. Instead, the C—B bond adds across the multiple bond to form phenylalkyl-(alkenyl) boranes.466,468... 

The best copper reagents are RCu.MgHlg2 and R2Cu.MgHlg derived from Grignard reagents, and R2CuLi (R = primary alkyl). Acetylene is the most reactive alkyne,515 whereas internal acetylenes do not react. 

Rhenacyclobutadienes are more stable toward loss of an acetylene or further reaction with an internal acetylene than other metallacyclobutadienes268-269,278 519. However, whereas the low-temperature l3C NMR spectra (-50 °C) of the rhenacyclobutadienes are consistent with their X-ray structure, coalescence of the ring signals is observed at room temperature, indicating a rapid exchange of the ReC3-ring carbons. Since no loss of acetylene is observed, this was attributed to a rapid equilibrium of the rhenacyclobutadienes with their -cyclopropenyl counterparts (equations 249 and 250)268,269,319. 

The rhenium carbyne complex Re(=CCMe3)(=NAr)(OR)2 is active for metathesis of internal acetylenes when OR is OCMe(CF3)2, but not when OR is OCMe2CF3, OCMe3 or OC6H3-i-Pr2-2,65 6. The complex W(=CMe)(Cl)(PMe3)4 undergoes stoichiometric metathesis with PhC=CPh but the product PhC=CMe remains coordinated to the metal centre759. 

Internal acetylenes, Ni-mediated reactions, 10, 546 Internal alkenes, ethylene co-polymers, 4, 1145 Internal alkynes in alder-ene reaction, 10, 567 intermolecular hydrosilylation with ruthenium, 10, 802 with yttrium, 10, 801 silylboration, 9, 163 silylformylation, 11, 483... 

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