Propargyl bromide addition

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. 

Little is known about the tolerance of 1 with unsaturated (poly)halogen compounds. Hydrozirconation of chloroalkenes can lead to competitive cycUzation, and simple reduction of both C=C and C-Cl bonds [98, 222], However addition of 1 to an alkenyl- or propargyl bromide led to the expected product as the sole product of the reaction in excellent yield (Scheme 8-30) [134, 223]. 

Diterpenoids related to lambertianic acid were prepared by intramolecular cyclization of either an alkene or an alkyne with a furan ring <2005RJ01145>. On heating amine 101 with allyl bromide, the intermediate ammonium ion 102 was formed which then underwent [4+2] cycloadditions in situ to give the spiroazonium bromides 103 and 104 (Scheme 13). These isomers arose from either endo- or co-transition states. The analogous reaction was also carried out with the same amine 101 and propargyl bromide. The products 105 and 106 contain an additional double bond and were isolated in 58% yield. The product ratios of 103 104 and 105 106 were not presented. 

The formation of an allenyl ketone as the sole product can be achieved by using an excess (2 equiv.) of propargyl bromide (entries 3—6, Table 5.9). Use of an increased amount (3 equiv.) of the acylzirconocene chloride in the reaction with propargyl bromide and/or tosylate yields a significant amount of a 1,4-dicarbonyl compound derived from Michael-type addition of the acylzirconocene chloride to the initially formed allenyl ketone (entry 2, Table 5.9). The Michael-type addition of acylzirconocene chlorides to allenyl ketones under Cu(I)-catalyzed conditions has been confirmed by an independent experiment (Scheme 5.31). 

The alkenylboronic esters were synthesized according to a literature procedure [56], Hydrozirconation of alkenylboronic esters with zirconocene hydrochloride, Cp2Zr(H)Cl, prepared by Buchwald s procedure [57], took place smoothly in CH2C12, providing in each case the corresponding borazirconocene 1,1-alkane 18 [34], Addition of propargyl bromide and a catalytic amount of copper(I) cyanide was accompanied by the disappearance of the yellow color associated with these compounds and by carbon—carbon bond... 

Propargyl bromide reacts with tributylstibine to form an intermediate allenylstibi-nate (A) (Table 9.62) [124], This intermediate fails to react with aldehydes at temperatures as high as 120 °C. However, addition of BuMgBr produces a reactive alleny-lantimony reagent (B), which reacts with aldehydes to yield homopropargylic alcohols. 

Recently, Hanzawa et al. reported that, catalyzed by Cu(II), the reaction of an acylzirconium with propargyl bromide affords 1,2-allenyl ketones 428, which may undergo a further conjugate addition with acylzirconocene to give 2-methylene 1,4-diketones 429 [191],... 

Fig, 18 Regioselective cathodic addition of propargyl bromides to aldehydes [106]. 

Diisopropylamine (0.12 mol, dried by shaking with machine-powdered KOH and subsequent distillation of the decanted liquid) is added overa few min to a solution of 0.12 mol of BuLi in 84 ml of hexane and 90 ml of Et2<) (a solution of EtLi.LiBr prepared as described in ref. 1 may be suitable as well) with cooling below O C. The obtained solution is cooled to below -80 C and freshly distilled propargyl bromide (0.10 mol, see Chap. XII, exp. 1.1) is added dropwise over 5 min while keeping the temperature between -75 and -80 C (a cooling bath with liquid N2 is indispensable). After an additional 5 min (at -80 C) the clear solution is ready for further reactions. 

HC=CCH=CHCH2Br, b.p. 40 C/15 mmHg, nD(20 ) 1.5350 (E.Z -85 15), is obtained in -70% yield by a similar procedure from the corresponding alcohol (p. 64). During the addition of PBr3 the solution turns very dark. The enyne bromide is a very lachrymatory compound. Contact of the liquid or vapour with the skin has a similar effect as in the case of propargyl bromide and other acetylenic bromides. 

Since propargyl bromide is readily ammonolysed, one should carry out this addition as quickly as possible. 

---