1-pentyne, reaction

Dimethylfuran, in a sensitized reaction, gave 1,3-dimethylcyclopropene (the main product), isoprene, cis- and rran.s-l,3-pentadiene, 2-pentyne, and 1-methylcyclopropenyl methyl ketone (Scheme 7) (70JPC574) the ring contraction showed a high selectivity. 

Ketones react with acetylide ion (Section 8.7) to give alcohols. For example, the reaction of sodium acetylide with 2-butauone yields 3-methy -l-pentyn-3-ol ... 

Johnson s classic synthesis of progesterone (1) commences with the reaction of 2-methacrolein (22) with the Grignard reagent derived from l-bromo-3-pentyne to give ally lie alcohol 20 (see Scheme 3a). It is inconsequential that 20 is produced in racemic form because treatment of 20 with triethyl orthoacetate and a catalytic amount of propionic acid at 138 °C furnishes 18 in an overall yield of 55 % through a process that sacrifices the stereogenic center created in the carbonyl addition reaction. In the presence of propionic acid, allylic alcohol 20 and triethyl orthoacetate combine to give... 

The metathesis of linear alkynes has also been reported, e.g. the metathesis of propyne, 1-pentyne, 2-pentyne, and 2-hexyne (31-33). This reaction can be visualized as the cleavage and formation of carbon-carbon triple bonds ... 

The formation of the tricarbonylchromium-complexed fulvene 81 from the 3-dimethylamino-3-(2 -trimethylsilyloxy-2 -propyl)propenylidene complex 80 and 1-pentyne also constitutes a formal [3+2] cycloaddition, although the mechanism is still obscure (Scheme 17) [76]. The rf-complex 81 must arise after an initial alkyne insertion, followed by cyclization, 1,2-shift of the dimethylamino group, and subsequent elimination of the trimethylsilyloxy moiety. Particularly conspicuous here are the alkyne insertion with opposite regioselectivity as compared to that in the Dotz reaction, and the migration of the dimethylamino functionality, which must occur by an intra- or intermo-lecular process. The mode of formation of the cyclopenta[Z ]pyran by-product 82 will be discussed in the next section. 

The benzannulation reaction with small alkynes such as 1-pentyne may generate a two-alkyne annulation product. In this case the original [3+2+l]-benz-annulation is changed to a [2+2+1+1]-benzannulation. After CO dissociation and insertion of the first alkyne, the coordinated a,/J-unsaturated moiety in the vinylcarbene complex is supposed to be replaced by the second alkyne. The subsequent reaction steps give the phenol 112 (Scheme 50). 

The Rh and Ir complexes 85-88 (Fig. 2.14) have been tested for the intramolecular hydroamination/cyclisation of 4-pentyn-l-amine to 2-methyl-1-pyrroline (n = 1). The reactions were carried out at 60°C (1-1.5 mol%) in THF or CDCI3 The analogous rhodium systems were more active. Furthermore, the activity of 87 is higher than 85 under the same conditions, which was attributed to the hemilabihty of the P donor in the former complex, or to differences in the trans-eSects of the phosphine and NHC ligands, which may increase the lability of the coordinated CO in the pre-catalyst [75,76]. 

Figure 4. Pd 3d5/2 binding energies of (a) Pd(l 11), (b) Pd foil, and (c) 5% Pd/CNT in the reaction mixture of 0.85 mbar H2 + 0.05 mbar 1-pentyne at 358 K. (Reprinted from Reference [65], 2006, with permission from Elsevier).

With terminal alkynes, the direction of the reaction depends on the nature of the substituent, the type of amine and the catalyst. Thus, dialkylamines can react with propyne to give 4-dialkylamino-4-methyl-2-pentynes traced from the Hy regioselec-hve formation of 2-dialkylaminopropene, i.e. the Markovnikov hydroaminahon product (Scheme 4-11) [256]. 

Pentyn-l-ol has been prepared from 4-penten-l-ol3 by bromi-nation followed by dehydrobromination with alkali,7 by the reaction of 3-bromodihydropyran with w-butylsodium or w-butyl-lithium,6 8 by the reaction of 2-methylenetetrahydrofuran with w-amylsodium or w-butyllithium,8 and by the method used in this preparation.9... 

Allenyldibromoborane was obtained in 34% yield by the reaction of boron tribromide with allenyltributylstannane below -80 °C [28], Allenyldimethylborane was likewise prepared in 84% yield from dimethylboron bromide. In neither case was the propargylborane observed. Both allenylboranes react with acetone to yield 2-methyl-4-pentyn-2-ol after hydrolysis (Eq. 9.25). 

The reaction of perfluoropenta-1,2-diene with cesium fluoride in foramide led to nonafluoropent-2-ene [58]. With anhydrous CsF the reaction in the vapor phase affords perfluoro-2-pentyne with MeOH, the reaction affords l-methoxy-2-per-fluoropentyne and l-methoxy-2H-octafluoro-2-(Z)-pentene [58]. 

With pentynes 4 or 5, a similar reaction was possible with potassium hydroxide at 175 °C here, depending on the reaction time and the temperature, between 2 and 13% of 1,2-pentadiene 6 could be obtained along with the pentynes (Scheme 1.3) [23],... 

Crucially, it was found22 that upon reaction of the vinylketene complex 42.a with 1-pentyne, the same product distribution was seen as for the direct thermolysis of 1-pentyne with the precursor carbene 43.a. The analysis was simplified by reduction of the crude reaction mixture with McMurry s reagent to produce a mixture of the isomeric indanols 44-46. 

The indanols 44 and 45 can only be the products of a formal [4 + 2] cycloaddition23 of the vinylketene complex 42.a with 1-pentyne. Note that upon reaction of 42.b with diethylpropynylamine a formal [2 + 2] cycloaddition65 is seen to take place, yielding the cyclobutenone 47 along with a tricarbonylchromium complex, tentatively identified as 48.66,67 As one would expect, the vinylketene complex 42.b underwent 1,2-additions with pyrrolidine and sodium methoxide in methanol, yielding 49 and 50, respectively. The CO-insertion step leading to vinylketene formation is reversible in some systems,51,68,69 but there is no evidence of this for complex 42.a. Heating a benzene solution of complex 42.a at 80°C under an atmosphere... 

The above-mentioned iridium complex, C4, as well as [ lr[bis(l-methylimidazol-2-yl)methane (CO)2][BPh4] (C5), also appeared very efficient in a one-pot tandem hydroamination/hydrosilylation reaction of 4-pentyn-l-amine with HSiEts to form 2-methylpyrroline, and then subsequently l-(triethylsilyl)-2-methylpyrrohdine with an essentially quantitative yield (Equation 14.5) [54]. 

The reaction of 77 with alkynes has further been elaborated for the synthesis of substituted phthalonitriles 81. An alternative for the synthesis of these compounds is the cycloaddition reaction of 77 with enamines followed by a retro-Diels-Alder loss of N2 and elimination of the amine (Scheme 16). Generally, more forcing reaction conditions are required and lower yields are obtained in reactions with alkynes than in reactions with enamines, for example, 4-ethyl-5-methylphthalonitrile is obtained in 51% yield from 2-pentyne (xylene, 150°C, 18 days) and in 73% yield from 4-(l-ethylprop-l-en-l-yl)morpholine (CHCI3, 70°C, 7 days) <1998T1809>. The mechanism of the reaction with enamines has been studied in detail. This revealed a [1,5] sigmatropic rearrangement in the cyclohexa-2,4-dien-1-amine intermediates formed after the loss of N2 <1998T10851>. 

A solution of 2.5 mol of sodium acetylidc in liquid NHj (p. 17-19) is cooled to —40 C and a vigorous stream of acetylene is introduced for 2 min (31/mjn). The alkyl bromide (2.0 mol) is then added dropwise over 1 h while maintaining the temperature as close as possible to -38 C Stirring at this temperature is continued for another 1.5 h (for the type of stirrer see fig 3), then 300 ml of high-boiling petroleum ether (b.p. >170 C) is added. The mixture is cautiously poured onto 2 kg of finely crushed ice in a 5-1 wide-necked round-bottomed (fig. 13) or conical flask. The reaction flask is rinsed with a small amount of ice water which is added to the bulk. After separation of the layers, three extractions with small amounts of petroleum ether are carried out The extracts are washed with dilute hydrochloric acid and subsequently dried over MgS04. Isolation is carried out as described in exps. 1 and 3, and in Chap. 1-2.6. The product is carefully redistilled through a 40-cm Widmer column. 1-Pentyne, b.p. 

In the preparation of 1-pentyne and 1-hexyne (exp. 10) complete conversion of the alkyl bromides is effected by using an excess of sodium acetylide. A reasoning based on economics prompts the use of an excess of the alkyl halide if alkali vinylacetylide or alkali diacetylide (generated from alkali amide and dichlorobutene or dichlorobutyne, respectively) are to be alkylated. If slightly mare than the stoichiometiical amount of alkyl bromide is used, no serious separation problems will be encountered during the final distillation. A relatively small amount of DMSO is added to enhance the solubility of the alkyl bromides, thereby facilitating the alkylation reaction. 

Although silylformylation of 3-butyn-I-ol 84 gives normal product 85 preferentially in the absence of EtsN, an appreciable amount (38%) of 7-lactone 86 is formed concomitantly." Protection of the hydroxy group in 84 leads to selective silylformylation of the acetylenic moiety as shown in Scheme 3. Hydrolysis of the silyl ether in 88 gives 85 as a single product. 4-Pentyn-I-ol 89 reacts with Mc2PhSiH under CO pressure to give a mixture of silylformylation product 90 (20%) and (5-lactone 91 (38%) after a short reaction time (0.5 h) (Equation (16)). The unusual lactone formation is not observed in the reaction of 5-hexyn-l-ol 92 in the presence of EtsN (Equation (17)). ... 

Radical carbonylation reaction serves as a powerful tool for the synthesis of a range of carbonyl compounds. Radical carbonylation has been successfully applied to the synthesis of functionalized ketones from alkyl, aryl, and alkenyl halides.The radical aminocarbonylation reaction of alkynes and azaenynes provided efficient routes to 2-substituted acrylamides, lactams, and pyrrolidinones. For example, the aminocarbonylation of 4-pentyn-l-yl acetate 318 initiated by tributyltin hydride (Bu"3SnH) (30mol%) with AIBN (20mol%) gave acrylamide 325 in 92% yield (Scheme 43).A proposed mechanism starts from the addition of tributyltin radical 319 to alkyne... 

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