Bromides propargyl

Svndiesis (Crombie, J. Chem. Soc. (C), 1969, 1016). The acetylenic bromide corresponding to allyl bromide is called propargyl bromide and is reactive and readily available. We shall need to protect the ketone before we make the acetylene anion. It turns out tliat protection and decarboxylation can be done in one step. 

Acetylenes can be hydrated to give ketones (frame 145) so propargyl bromide must provide a MeCOCH2 synthon ... 

Similar experiments with propargyl bromide failed. 

Ojj 1.5323, prepared from phenol, KOH in ethanol and propargyl bromide) was added and the mixture was heated at 60°C for 15 min. It was then poured into 200 ml of ice-water and the reaction products were extracted with diethyl ether. The ethereal extracts were washed with saturated NH Cl solution, dried over magnesium sulfate and then concentrated in a water-pump vacuum. There remained 9.5 g of 3 1 mixture... 

In the first method a secondary acetylenic bromide is warmed in THF with an equivalent amount of copper(I) cyanide. We found that a small amount of anhydrous lithium bromide is necessary to effect solubilization of the copper cyanide. Primary acetylenic bromides, RCECCH Br, under these conditions afford mainly the acetylenic nitriles, RCsCCHjCsN (see Chapter VIII). The aqueous procedure for the allenic nitriles is more attractive, in our opinion, because only a catalytic amount of copper cyanide is required the reaction of the acetylenic bromide with the KClV.CuCN complex is faster than the reaction with KCN. Excellent yields of allenic nitriles can be obtained if the potassium cyanide is added at a moderate rate during the reaction. Excess of KCN has to be avoided, as it causes resinifi-cation of the allenic nitrile. In the case of propargyl bromide 1,1-substitution may also occur, but the propargyl cyanide immediately isomerizes under the influence of the potassium cyanide. 

Note 2. This operation is necessary to remove the propargyl bromide. At higher temperatures bromoallene also reacts with the amine. 

Note 2. Propargyl bromide itself also reacts with ammonia and therefore the interval between the addition of this compound and its conversion with the enethiolate should be kept as short as possible. Inverse addition was applied if propargyl bromide is added to the enthiolate solution, the primary product partly isomerizes into H2C=C(5C2Hs)SCH=C=CH2 under the catalytic influence of the enethiolate. 

Note 3. During this period the excess of propargyl bromide is converted into propargylamines. 

A solution of 92 g of dry sodium iodide in 350 ml of 100% ethanol (note 1) was heated to about 70°C. Freshly distilled propargyl bromide (note 2) (0.50 mol) was added in 10 min. After heating for 20 min at 70-75°C the white suspension was cooled to room temperature and 500 ml of water were added, then the product was... 

Various halogenating agents have been used to replace hydroxyl with chlorine or bromine. Phosphoms trihaUdes, especially in the presence of pyridine, are particularly suitable (17,18). Propargyl iodide is easily prepared from propargyl bromide by halogen exchange (19). 

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)... 

Similarly alkylation (55) of l-N-pyrrolidino-2-methyl-l-propene (22) with propargyl bromide gave initial N alkylation to (23) with subsequent rearrangement to the allene (24). 

Brown et al. were not able to prepare 3-(prop-2-ynyl)indole [i.e., 3-propargylindole (49)] by the Grignard reaction however, Williamson and later Zenitz readily obtained 49 in satisfactory yield by the action of propargyl bromide on indole magnesium bromide in anisole. 

In mosl allylation reactions, only a catalytic amount of CuCN-2LiCl is required [41]. Use of die chiral ferrocenylamine 104 as a catalyst makes enables asymmetric allylation of diorganozinc reagents to be effected witli allylic chlorides iScbeme 2.3G) [78]. Related electropb des such as propargylic bromides [79] and unsaturated epoxides [80] also undergo Su2 -substitution reactions iScbeme 2.37). 

A mixture of 23.8 grams (0.2 mol) of propargyl bromide, 24.2 grams (0.2 mol) of N-methyl benzylamine and 400 ml of anhydrous ethanol in the presence of 42.4 grams (0.4 mol) of anhydrous sodium carbonate was heated at the boiling temperature and under reflux for a period of 17 hours. 

Propargyl Bromide (3-Bromo-l-propyne). HC=CCH2Br mw 118.97 colorl to faintly brownish liq mp 24.4° bp 88—90° d 1.52 g/cc RI 1.4320 at 20°. Sol in ale, eth, benz chlf. Flammable flash pt 10° (closed), 18° (open) ignition temp 328° lower flammable limit 3.0%. It can be decompd by mild shock. When heated under confinement, it decomps with expl violence and may detonate. When suitably diluted, as with 20—30% by wt of toluene, its expl properties are practically eliminated (Ref 4)... 

Pure propargyl bromide will dccomp violently or detonate at temps as low as 220° (Ref 2). Liq propargyl bromide is easily ignited by impact from such possible sources as water hammer or accidental pressurization of the accelerated liq (Ref 3). Tests at the BuMines showed a mixt of chloropicrin and propargyl bromide to be shock sensitive (Ref 3)... 

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