Allenylmagnesium bromide

In that case the rate of stirring should be reduced until the solid has disappeared. 

The solution contains about 0.5 mol of allenylmagnesium bromide. This estimation is based upon the results of several derivatization reactions carried out in the laboratory (compare also Refs 6 and 7). Reaction at room temperature with Me3SiCl (0.5 mol, 54.3 g), followed by aqueous hydrolysis, gives a mixture of Me3SiCH2C=CH and Me3SiCH=C=CH2 (ratio 92 8), b.p. 92 °C/760mm, in an excellent yield. 

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To prepare the other cross-conjugated allene, 4-methylene-l,2,5-hexatriene ( 2-allenyl-1,3-butadiene ) (23), the allene alcohol 215 was first converted into the phosphate 216, that readily underwent an SN2 -type substitution with allenylmagnesium bromide to yield the target hydrocarbon as a highly reactive allene derivative (Scheme 5.32) [76],... 

An alternative transmetallation procedure employs Grignard reagents, such as allenylmagnesium bromide, which reacts with Bu2SnCl2 in ether to afford dibutyl-... 

Surprisingly, only a single application of a copper(I)-catalyzed cross-coupling of metallated allenyl species has been reported [44]. The CuBr-catalyzed coupling of allenylmagnesium bromide (82) with allyl phosphate 83 provided 6-butyldeca-l,2,5-triene (84) in high yield, as depicted in Eq. 14.8. 

A solution of about 0.5 mol of allenylmagnesium bromide in -400 ml of Et20, prepared as described on p. 35, is cooled to - -40 C. The aldehyde (0.50 mol, freshly distilled, note 1) is then added dropwise over 20 min with vigorous stirring. After the addition, the temperature is allowed to rise from -40 to +10 C. In most cases a coarse suspension is formed. The reaction... 

In general, this synthesis of enynes has no special advantages over the alternative method which starts with allenylmagnesium bromide [144] ... 

Some unreacted magnesium turnings remain in the flask at this time. However, the submitters recommend against heating the mixture to achieve further conversion, since the initially formed allenylmagnesium bromide will isomerize to 1 -propynylmagnesium bromide. 

Allenylmagnesium bromide is converted to diallenyl dibutyltin upon treatment with Bu2SnCl2 in ether (Eq. 71) [85], This reagent undergoes ligand redistribution with additional Bu2SnCl2 to allenyldibutyltin chloride [86],... 

The tautomerism of hydroxythiazoles has been discussed in Section 3.06.4.4. The reactivity of hydroxythiazoles is well-documented in CHEC-I <84CHEC-I(4)285>. 2-Methoxy benzothiazole (184) has been found to react with allenylmagnesium bromide (185) to produce 2-allenylbenzothiazole (188), the formation of which can be rationalized in terms of a Sgi mechanism involving the attack of the allenic form of the Grignard reagent followed by the elimination of methanol and isomerization of the intermediate (187) (Scheme 44) <86S638>. 

Organometallics of allenic structure are usually prepared by the reactions of metals with propargylic or allenic halides, or by metallation with alkyllithiums of the corresponding hydrocarbons. The first preparation of allenylmagnesium bromide was accomplished by Prevost in I950. Allenylzinc bromide is easily obtained by the direct reaction of the metal with propargyl bromide at -100 °C in anhydrous tetra-hydrofuran. The yield is greater than 80%. ... 

Reaction with boronates and aryUrismutii triflates. Dialkyl 2,3-butadienylboronates, which serve as l,3-butadiene-2-yl anion equivalents, are formed from allenylmagnesium bromide with dialkyl (halomethyl)boronates. ... 

Brown and coworkers [3,4] discovered that B-allenyl-9-BBN [3] readily prepared from B-chloro-9-BBN [5] and allenylmagnesium bromide [6] (Eq. 6.13) undergoes a facile condensation with aldehydes and ketones to yield exclusively the corresponding homopropargylic alcohols in excellent yields [3, 4]. B-Alle-... 

Comparative studies of these pairs with allenylmagnesium bromide (Table 6.15) [3] establishes that the Grignard reagent is much less chemoselective. 

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