Propyne preparation

L,2-propadiene, allene, CH2=C = CH2, CjH4. Colourless gas prepared by the electrolysis of potassium itaeonate, or by the action of zinc and alcohol on 1,3-dibromopropane. It is easily isomerized to propyne (methylacetyl-ene), and is produced as a mixture with this substance from some reactions. 

A suspension of di1Ithiopropyne in THF and hexane was prepared from 0.25 mol of propyne (see Chapter II, Exp. 17). The suspension was cooled to -10°C and 0.22 mol of benzyl chloride was added dropwise in 30 min, while maintaining the temperature of the mixture at about -10°C. The cooling bath was then removed temporarily and the temperature was allowed to rise to After stirring for... 

To a solution of ethylnagnesium bromide in 350 ml of THF, prepared from 0.5 mol of ethyl bromide (see Chapter 11, Exp. 6) was added in 10 min at 10°C 0.47 mol of 1-hexyne (Exp. 62) and at 0°C 0.47 mol of trimethylsilylacetylene (Exp. 31) or a solution of 0.60 mol of propyne in 70 ml of THF (cooled below -20°C). With trimethyl si lylacetylene an exothermic reaction started almost immediately, so that efficient cooling in a bath of dry-ice and acetone was necessary in order to keep the temperature between 10 and 15°C. When the exothermic reaction had subsided, the mixture was warmed to 20°C and was kept at that temperature for 1 h. With 1-hexyne the cooling bath was removed directly after the addition and the temperature was allowed to rise to 40-45°C and was maintained at that level for 1 h. 

A suspension of 0.35 mol of sodium amide in 400 ml of liquid ammonia was prepared in the usual way (e./. Chapter II, Exp. 11) (note 1). To this suspension was added with swirling 0.30 mol of 1-methylthio-l-propyne, in portions of about 10 g, waiting about 10 s after the addition of each portion. Swirling was continued for 1.5 min after the addition of the last portion. Immediately thereafter the... 

Alkynes with EWGs are poor substrates for the coupling with halides. Therefore, instead of the inactive propynoate, triethyl orthopropynoate (350) is used for the coupling with aryl halides to prepare the arylpropynoate 351. The coupling product 353 of 3,3-dicthoxy-l-propyne (352) with an aryl halide is the precursor of an alkynal[260]. The coupling of ethoxy) tributylstan-nyl)acetylene (354) with aryl halides is a good synthetic method for the aryl-acetate 355[261]. 

Show by writing an appropriate series of equations how you could prepare propyne from each of the following compounds as starting mate rials You may use any necessary organic or inorganic reagents... 

Assume that you need to prepare 4 methyl 2 pentyne and discover that the only alkynes on hand are acetylene and propyne You also have available methyl iodide isopropyl bromide and 1 1 dichloro 3 methylbutane Which of these compounds would you choose in order to perform your synthesis and how would you carry it out" ... 

At low temperatures, oxidation with chromic acid gives propynal [624-67-9] C2H2O (14), or propynoic acid [471-25-0] C2H2O2 (15), which can also be prepared in high yields by anodic oxidation (16). 

Isothiazole itself is best prepared by the reaction between propynal, ammonia and sodium thiosulfate (see Section 4.17.9.3). A wide range of substituted mononuclear isothiazoles can be obtained by oxidative cyclization of y-iminothiols and related compounds (see Section 4.17.9.1.1). Substituents at the 3-position need to be in place before cyclization, but 4-substituents are readily introduced by electrophilic reagents (see Section 4.17.6.3), and 5-substituents via lithiation (see Section 4.17.6.4). 

How would you prepare cis-2-butene starting from propyne, an alky) halide, and any other reagents needed This problem can t be worked in a single step. You ll have to carry out more than one reaction. 

Evidence for the occurrence of vinyl cations as short-lived intermediates in solvolysis and other reactions has accumulated in the last few years (reviewed by Hanack, 1970, by Richey and Richey, 1970, and by Modena and Tonellato, 1971), but they have not been observed spectroscopically. It has been shown possible to intercept some vinyl cations—prepared in a system of extremely low nucleophilicity (EHSO3—SbEj 1 1-1 10) by protonation of propyne and 2-butyne— by carbon monoxide (Hogeveen and Roobeek, 1971b). The oxocarbo-nium ions formed in these cases are shown in the following scheme ... 

Trialkyl- or triarylallenyltin compounds can also be prepared by Sn2 displacement of propargylic mesylates with various stannylcopper reagents in THF (Eq. 9.82) [71]. This reaction is postulated to proceed by an anti Sn2 pathway based on the stereochemical relationship between the enantioenriched mesylate and the allenic product (Eq. 9.83). The allene obtained from the reaction of the mesylate of (R)-3-phenyl-l-propyn-3-ol with Ph3SnCu was assigned the (P) configuration from a consideration of the observed optical rotation and an application of Brewster s rules [71]. 

The reaction leading to 20 was used to prepare 25 (Scheme 3.2-13) [35], starting from diethyl(propyn-l-yl)borane which served as a versatile reagent for the synthesis of other carboranes (vide infra). l,l-Bis(diethyl-boryl)propene 23 can be detected and isolated, whereas it was not possible to identify l,l,l-tris(diethylboryl)propane 24 in the reaction mixture. 

Hatch. L.F. and Kidwell, L.E., Jr. Preparation and properties of 1-bromo-l-propyne, 1.3-dibromopropyne and l-bromo-3-chloro-l-prop3me, / Am. Chem. Soc., 76(l) 289-290, 1954. 

Although a two-step synthesis of l,l -(l,3-phenylene)bis-(3-phenyl-2-propyn-l-one) (1,3-PPPO) has been reported [8], we found that 1,3-PPPO could also be prepared from a one-step route, starting from iso-phthaloyl chloride and phenylacetylene, employ-... 

Benzofuranyl)pyrroles, 2-(2-thienyl)pyrroles , 2,2 -dipyrroles, 3-(2-pyr-rolyl)indoles , 2-(2-benzimidazolyl)pyrroles and2-(2-, 3- and4-pyridyl)pyrroles were prepared using this method. Reaction of alkynes (for example, propyne) or allene with ketoximes in a superbase system (MOH/DMSO) leads to 2,5-di- or 2,3,5-trisubstituted pyrroles Pyrroles and dipyrroles were synthesized also from corresponding dioximes and acetylene in a KOH/DMSO system It has also been shown that 1,2-dichloroeth-ane can serve as a source of acetylene in pyrrole synthesis. Oxime 52 in the system acetylene/RbOH/DMSO at 70 °C afforded a mixture of three pyrroles 53-55 in low yields (equation 23). The formation of product 53 occurred through recyclization of pyrrolopy-ridine intermediate. ... 

Copper(I) acetylide is used in a diagnostic test for CH unit to prepare pure copper powder in purification of acetylene and as a catalyst in the synthesis of acrylonitrile and 2-propyn-l-ol. 

Other synthetic methodologies have been used to prepare the unusual octahedral osmium(II) allenylidenes [OsH(=C=C=CPh2)(NCMe)2(PiPr3)2][BF4] and [Os k (C,0)-C(C02Me)=CH2 (=C=C=CPh2)C0)(PiPr3)2][BF4] from l,l-diphenyl-2-propyn-l-ol [22]. 

Preparation of alkenylcarbene metal complexes was reported by Le Bozec and Dixneuf et al. in 1991 by activation of propargylic alcohols in the presence of methanol [13[. Thus, photolysis of M(CO)6 (M = Cr, W) in the presence of 2-propyn-l-ol derivatives 30 in the presence of MeOH gave the corresponding... 

The catalytic propargylic alkylation was investigated in the presence of thiolate-bridged diruthenium complexes as catalysts generated in situ from reactions of [Cp RuCl(p2-Cl)]2 with optically active thiols prepared from the corresponding optically active alcohols [27]. Typical results for the reaction of 1-phenyl-2-propyn-l-ol with acetone in the presence of a variety of catalysts are shovm in Scheme 7.19. 

For synthetic purpose, the selective preparation of tetrasubstituted enynes was also investigated in the reactions of l-cydopropyl-2-propyn-l-ols bearing a substituent at the a-position in a cyclopropane ring with anilines (Scheme 7.37). As expected, the corresponding tetrasubstituted enynes were obtained in high yields with almost complete selectivity. 

Trimethylsilyl-2-propyn-l-o1 was obtained from Petrarch Systems, Inc. and used as received. Alternatively, it can be prepared by the silylation of 2-propyn-l-ol ... 

---