Propargyl chloride

A mixture of 0.40 mol of propargyl chloride and 150ml of dry diethyl ether was cooled at -90°C (liquid nitrogen bath) and a solution of 0.40 mol of ethyl-lithium (note 1) in about 350 ml of diethyl ether (see Exp. 1) was added with vigorous stirring and occasional cooling (note 2). The temperature of the reaction mixture was kept between -70 and -90°C. The formation of the lithium derivative proceeded almost instantaneously, so that the solution obtained could be used directly after the addition of the ethyl 1ithium, which was carried out in 15-20 min. This lithium acetylide solution is very unstable and must be kept below -60°C. 

Note 7. To a solution of 0.55 mol of sodium hydroxide in 150 ml of methanol and 40 ml of water was added a cold solution of 0.55 mol of methanethiol in 50 ml of methanol with cooling below 10°C. Subsequently 0.50 mol of propargyl chloride was added with swirling in 15 min, while keeping the temperature between 20 and 40°C. After an additional 30 min 1 1 of water was added and the product was extracted six times with small amounts of pentane. The extracts were washed with water, dried and the solvent was... 

Oq 1.4783, yield 84 ) was prepared by lithiating propargyl chloride with ethyllithium (see Chapter 11, Exp. 1 and 16) in diethyl ether and subsequently adding pivalyl aldehyde. 

With propargyl chloride a mixture consisting of about 85% of PhS-CH=C=CH2 and 15% of HC=C-CH2"SPh was obtained, when using catalytic amounts of CuBr. 

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

Propargyl chloride (3-chloropropyne) [624-65-7] M 74,5, b 58 /760mm, 65 /760mm, d 1.03, n 1.435. Purified by fractional distn at atm press. Note that a possible impurity propargyl alcohol has b 114-115°/atm. [Henry Chem BerS 398 1 875.] HIGHLY TOXIC and FLAMMABLE. 

When perfluoroheptylcopper reacted with propargyl bromide, a violent reaction occurred, and less than 10% of the expected allene was obtained [226] However, when propargyl chlorides or tosylates were used as substrates, the expected allenes were obtained m good yields [227] (equation 156)... 

Ruthenium hydride complexes, e.g., the dimer 34, have been used by Hofmann et al. for the preparation of ruthenium carbene complexes [19]. Reaction of 34 with two equivalents of propargyl chloride 35 gives carbene complex 36 with a chelating diphosphane ligand (Eq. 3). Complex 36 is a remarkable example because its phosphine ligands are, in contrast to the other ruthenium carbene complexes described so far, arranged in a fixed cis stereochemistry. Although 36 was found to be less active than conventional metathesis catalysts, it catalyzes the ROMP of norbornene or cyclopentene. 

The subsequent chain extension can be accomplished by the pedestrian step-by-step homologation sequence via the acyclic diyne 12 or by a more efficient block-to-block strategy. The step-by-step approach includes protiodesilylation of diyne 12 followed by coupling with the propargyl chloride 9 following the same protocol as for the preparation of 12 from 11 and subsequent repetitions of protiodesilylation and alkylation with chloride 9 to reach stages 16 and 18, respectively (Scheme 3). 

Ylide-derived products may be formed as minor by-products from propargylic chlorides or ethers this contrasts with the inertness of allylic chloride or ethers... 

Reduction to Halocarbons. The best conditions for the reductive chlorination of ketones use the reagent combination Me2ClSiH/In(OH)3 (Eq. 241).331 Examples include conversions of aryl ketones to benzyl chlorides, ethynyl ketones to propargyl chlorides, and alkyl ketones to alkyl chlorides (Eq. 242).331 Addition of lithium iodide to the reaction mixture yields the corresponding iodide product. The combination of TMDO/I2 reductively iodinates aryl ketones and aldehydes in good yields (Eq. 243).357... 

Hydride-promoted reactions are also well known, such as the acrylic and vinylacrylic syntheses (examples 7-10, Table VII). Some less-known compounds, which form in the presence of halide ions added to tetracar-bonylnickel, have been described by Foa and Cassar (example 11, Table VII). Reaction of allene to form methacrylates, and of propargyl chloride to give itaconic acid (via butadienoic acid), have been reported (examples 13 and 14, Table VII). 1,5-Hexadiene has been shown to be a very good substrate to obtain cyclic ketones in the presence of hydrogen chloride and tetracarbonylnickel (example 15, Table VII). The latter has also been used to form esters from olefins (example 16, Table VII). In the presence of an organic acid branched esters form regioselectivity (193). 

Solvolysis of the propargyl chlorides E- and Z-24 (stereochemistry based on Cl and Ph25) in 80% aqueous ethanol at 50 °C gave, besides the corresponding solvent captured substituted propargyl products, the allenyl chlorides E- and Z-25 formed with complete retention via the allenyl cation intermediate (equation 6)25. 

Similar to the cycloaddition of allyl cations30, allenyl cations have been found to undergo cycloadditions with alkenes to afford bicyclic compounds31. The allenyl cations were generated from propargyl chlorides by treatment with Lewis acids. This reaction sequence proceeds via the cyclization 34 -------> 3532, in spite of the fact that... 

The cycloaddition of allenyl cations with 1,3-dienes results in a number of intermediate cations from which different products result. The allenyl cations 38 are generated first by the reaction of propargyl chlorides with zinc chloride and are then allowed to react with cyclopentadiene or other 1,3-dienes. The products of cycloaddition depend on the substituents on the allenyl cations32,35. The products formed with cyclopentadiene are given in equation 14. 

In general, allenyl cations 38 attack at the sp2-carbon atom of 1,3-dienes and form vinyl cations 39 and 40 (R = H, alkyl) or (R = aryl). Although a concerted cycloaddition mechanism is possible, a stepwise mechanism is preferred34. If a nucleophilic attack at the sp-carbon atom of the allenyl cation takes place, then cation 41 and the resulting cations 42 and 43 are formed. Some examples of bicyclic products obtained from cyclic 1,3-dienes and propargyl chlorides are given in equation 1534. 

Propargyl alcohol, p249 Propargyl chloride, c241 Propenamide, a61 2-Propen-1-amine, a76... 

An alternative route to allenyl stannanes involves organocuprate displacements on propargylic chlorides bearing an alkynyl PhsSn substituent (equation 39)79. Interestingly, transmetallation by attack of the cuprate on the tin substituent is not observed in these systems. A parallel strategy can be employed for allenylgermanes (equation 39)79. The... 

Negishi first observed the insertion of the y-halolithium species 75 obtained by deprotonation of propargyl chloride into octylzirconocene chloride protonation of the product afforded the allene 79 (Scheme 3.20) [37]. The overall effect is insertion of an allenyl carbenoid. The a-halolithium equivalent 76 is conveniently generated by addition of two equivalents of base to 2-chloroallyl chloride [52] and affords the same products. The organome-tallic product 77 of allenyl carbenoid insertion is either in equilibrium with the propargyl... 

The reaction of propargyl chloride 83 and trichlorosilane 84 showed two different regioselectivities depending on the choice of transition metal catalysts [88]. Whereas the Sn2 substitution proceeded to give the propargylsilane 85 with 94% selectivity using a CuCl catalyst, the silylallene 86 was obtained via an SN2 pathway with >97% selectivity with 3mol% of Ni(PhCOCHCOPh)2 (Scheme 3.42). 

The reaction could be applied to propargyl chloride 174 and propargylamine 176 and corresponding allenes 175 and 177 were obtained in 63 and 85% yields, respectively (Scheme 3.89) [126],... 

Allenylboranes can also be prepared from lithiated propargyl chloride [20]. As noted above, these intermediates react with acetic acid to afford allenes (Table 9.11). 

Table 9.11 Synthesis of allenes from propargyl chloride.

Table 9.12 Conversion of lithio propargyl chloride to allenic carbinols and homopropargylic alcohols.

Allenyltrichlorosilanes can also be prepared by Sn2 displacement of propargylic chlorides with a Cu or Ni complex of HSiCl3 [56]. The reaction requires an amine base and a donor solvent such as THF or propionitrile (Table 9.32). Conditions can be adjusted to favor the propargylic or allenic silane, which is not isolated, but treated directly with various aldehydes to afford allenylcarbinols (A) or homopropargylic alcohols (B). These reactions presumably proceed by an SE2 pathway, such that the allenyl products arise from the propargylic silane and vice versa. 

The regioselectivity is maintained with mono- and even disubstituted propargylic chlorides (Table 9.33) [56], The copper complex affords allenylcarbinols (A) and the nickel complex favors homopropargylic alcohols (B). In the latter case, the syn adducts are predominant, suggestive of an acylic transition state. 

Chiral allenylpalladium complexes have been prepared from non-racemic propargylic chlorides and Pd2(dba)3-PPh3 [88]. Although nominally stable, these complexes were found to racemize under certain conditions (Eq. 9.108). Reagents prepared under oxygen-free conditions racemize more slowly than those prepared in... 

Scheme 9.23 Proposed structure for the dinuclear palladium complex derived from a chiral propargyl chloride.

Chlorination of simple allenes in CH2C12 with or without BF3 afforded a mixture of 2,3-dichloro-l-propene and propargyl chloride [11, 12]. 

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