Octynes, internal

The combination of [IrCl(cod)Cl]2 complex with P(t-Bu)3 efficiently catalyzes aromatic homologation using internal alkyne [70]. For example, the reaction of benzoyl chloride 153 with 4-octyne 154 afforded 1,2,3,4-tetrapropylnaphthalene 155 (Equation 10.41). The reaction with 2-thenoyl and 2-naphthoyl chlorides also affords benzothiophene and anthracene, respectively, in high yields. The reaction would proceed as follows (Scheme 10.9) (i) oxidative addition of aroyl chloride... 

The hydrophosphorylation of internal alkynes is somewhat slow. For instance, the reaction of 4-octyne with diethyl phosphonate resulted in 82% yield only after heating for 65 h. Only c/s-isomer was observed in NMR spectroscopy. 

AUyUdumination of alkynes.4 The reaction of allyldiisobutylaluminum, prepared from allylmagnesium bromide and i-Bu2A1C1, with 1-octyne in the presence of Cl2ZrCp2 results in ds-allylalumination to provide a mixture of two regioisomers, 1 and 2. Internal... 

Reaction (d) occurs for terminal alkynes (R = H), 1-hexyne, 1-octyne and phenyl acetylene (80-98%), with no further reduction to alkanes . The internal alkynes, 2-hexyne and diphenylacetylene, give exclusively cis-alkene (80-95%) ". However, the organometallic intermediates of Eq. (d) may contain Cu—C rather than Mg—C bonds. 

Halogenation of vinylboranes generates vinyl halides. Both cis and trans halides are available by modification of the reaction conditions. When trans-alkenyl boronic acid (73, derived from 1-octyne) was treated with iodine and sodium hydroxide, trans-1-iodo-l-octene (74) was formed in 90%. When the boronic acid was treated with iodine and then with base, the (Z)-alkenyl iodide (75) was produced.Vinylboranes derived from internal alkynes lead to cis-trans mixtures with both of these procedures. Boronic acids derived from alkynes and catecholborane give the (Z)-bromide on addition of bromine followed by sodium hydroxide. ... 

Terminal alkynes are more reactive than internal alkynes, presumably because they are more strongly adsorbed thus 1-octyne has been reduced to 1-octene in the presence of 4-octyne, which remained unaffected. "... 

Hydrophosphinylation of 1-octyne with diphenylphosphine oxide (105) afforded the alkenylphosphine oxide 106 by internal attack with high regioselectivity. However, addition of a small amount of Ph2P(0)OH changed the regioselectivity to provide the product 107 by terminal attack [32]. 

Borylsilylation of 1-octyne with 120 provided the alkenylboronate 121 in high yield using Pd(OAc)2 and bulky isocyanide (1,1,3,3-tetramethylbutyl isocyanide, XVll-6) as a ligand. The product 121 was subjected to Suzuki coupling catalyzed by PdCBCdppf) [36], Under similar conditions, no intermolecular bis-silylation of internal alkynes took place. However, intramolecular bis-silylation of disilanyl ether of homopropargylic alcohol proceeded smoothly with 5-exo-dig cyclization [36a]. 

Already in 1977 Inoue discovered the reaction of hexynes with carbon dioxide catalyzed by nickel complexes [86]. 1-Hexyne reacted with CO2 in the presence of a nickel/dppe-catalyst to give the butyl-substituted pyrone in 50 % yield (Figure 31). As by-products the oligomers of 1-hexyne were formed. Similar reactions proved to be possible with alkynes containing internal double bonds, such as 3-hexyne and 4-octyne [87,88], giving tetrasubstituted pyrones. Yields up to 60 % could be obtained. 

The same reaction was performed in the presence of a source of Pd and a bidentate phosphine in toluene at 50 °C. Methylphenylphosphine borane (41a) was reacted with 1-octyne in the presence of palladium acetate (5%) and dppp (10%) for 35 minutes. Interestingly, the Markovnikov product 43a is obtained in 85% yield, with no trace of 42, meaning that in this case the phosphorus attacks the internal carbon of 1-octyne. The same reaction using bdpp (2,4-dw(diphenylphosphino)pentane) and phenylacetylene (39, R = Ph) also yields regioisomer of 43 with 53% yield. Several experiments with diphenylphosphine borane under different reaction conditions (palladium source, temperature, alkyne) showed that the reaction does not occur in the absence of palladium (0) and that hydrophosphination of 1-ethynylcyclohexene (42) undergoes selective hydrophosphination at the triple bond, with the alkeneic bond untouched. 

Terminal alkynes exhibit C = C — H stretching at 3300 cm. This absorption band is absent in internal alkynes, because the triple bond is not bonded to a proton. All alkynes absorb weakly between 2100 and 2260 cm due to C = C stretching. This stretching shows clearly in the spectrum of 1-octyne (Figure 11.6). 

The monomer solution is prepared by adding 1-chloro-l-octyne (6.0 mmol, 0.87 g, 0.95 mL), dodecane (0.35 mL as internal standard of GC), and toluene... 

Internal alkynes such as diphenylacetylene and phenylpropyne were less reactive, but the borylstannation proceeded smoothly at 80 °C to give the corresponding cw-addition products. The borylstannane Me3SnB(NEt2)2 also reacted with various alkynes very similarly to 2. However, the resulting adducts were somewhat thermally unstable and attempted isolation by distillation resulted in deterioration of the products. The catalysis is envisioned to be triggered by oxidative addition of the B—Sn bond. X-ray structure of the complex derived from 2 and Me2Pd(dmpe) has been determined and the complex was found to react with 1-octyne to afford the borylstannation product (see Sect, n.2.6). 

N-Annulation of a,(3-enone with internal alkyne To a MeOH solution (0.2 mL) of 2-methyl-5-methylenenonan-4-one (33.7 mg, 0.20 mmol) and 4-octyne (44.1 mg, 0.40 mmol) were added [Cp RhCl2]2 (3.1 mg, 0.005 mmol) and Cu(OAc)2 H2O (79.9 mg, 0.40 mmol), NH4OAC (30.8 mg, 0.40 mmol), and the reaction mixture was stirred at 130°C under a nitrogen atmosphere for 6h. After cooling to room temperature, the solvent was removed in vacuo, and the resulting erude mixture was subject to flash column chromatography (n-hexane ethyl acetate = 90 1) to afford 3-butyl-2-isobutyl-5,6-dipropylpyridine (51.8 mg, 0.188 mmol) in 94% yield. 

The reaction has been extended to internal alkynes as substrates (Scheme 1.44) [12]. Under slightly milder conditions, almost full conversion was noted. Most of the a,P-unsaturated aldehydes formed were obtained in good to excellent yields. Interestingly, with the terminal alkyne 1-octyne, a-hexyl acrolein was obtained only in 17% yield. In unsymmetrically substituted alkyl-aryl-alkynes, the formyl group was predominantly linked to the neighboring aryl substituent. Bulky alkyl groups forced the C-C bond formation reaction in the P position. 

Most of the catalytic reactions require a certain minimum temperature. Irrespective of pressure, no reaction occurs below this temperature. This temperature, e.g., is 180 to 183 °C for n-octyne and 198 to 200 in the case of internal octynes [146]. The effect of temperature on the reaction velocity at different catalyst concentrations was investigated by a number of authors [410-413]. 

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