Crotyl halide

Homoallylic alcohols (8, 111-112). CrCl2, prepared in situ by reduction of CrCl, (Strem) in THF with Na/Hg, is superior to CrCl2 prepared by reduction of CrCl, with LiAlHj for the Cr(II)-mediated addition of crotyl halides to aldehydes. The homoallylic alcohols are formed in good yield and with high arm-selectivity.7 Example ... 

A number of allylic chlorides have been reported to yield photoproducts characteristic of the alkene moiety and not of the C—X bond123. Allyl and crotyl halides undergo photochemical reactions with chromium, molybdenum and tungsten complexes, which involve C—X bond cleavage133. 

The formation of olefinic nitriles from allylic halides is best accomplished with dry, powdered cuprous cyanide rather than with alcoholic alkali cyanides, with which side reactions such as isomerization and alcoholysis of the double bond are particularly bothersome. With cuprous cyanide the yields in the synthesis of allyl cyanide and methal-lyl cyanide are 84% and 86%, respectively. Higher allylic halides are subject to allylic rearrangements thus cuprous cyanide acts on crotyl halide (CH,CH CHCHjX) and methylvinylcarbinyl halide (CH,CHXCH = CH,) to produce the same mixture of isomeric nitriles (9 1) regardless of which halide is treated. Numerous cyanides of the allylic type (Cj-Ci4) have been prepared, although the possibility of an isomerization has not been considered. A similar isomerization has been observed in the reaction of sorbyl chloride and potassium cyanide. ... 

Yields of alcohols vary from 45 to 87%, irrespective of solvent or halogen type. However, when crotyl halides are used, 1-methylallyl products are isolated [20], along with occasional diaddition products [Eq. (2)]. 

Crotyl halides C HaC H = C H-C Ha-X react with nickel tetracarbonyl to give crotyl nickel halides [(A3-C4H7)NiX]2. Carbon-13 NMR spectra showed (40, 213) that on complexation to nickel C(2) and C(3) were shifted upheld whilst C(l) was shifted downfield. The shieldings for the /fS-allylic carbons were C(l) > C(3) > C(2). (See Table XLVI.) The methyl, C(4) and C(2) resonances were found to be nearly independent of the nature of the halogen (213) whilst C(2) varied over the range 6.2 ppm for X = Cl, Br, I. Jc-h coupling constants were also measured in this work (Table XLVI). The authors con-... 

It must be stressed that in the sulfur series, the reaction of crotyl halides takes place regioselectively, leading to S-crotyl derivatives (examples [42, 47]). The oxygen series stand in contrast, with reactions of enolates proceeding on the carbon atom, and not on oxygen. Furthermore, it is not regioselective with crotyl-type halides. 

From the results, presented in Table 2.10, it can be concluded that Barbier reactions with crotyl halides are much less promising when propanal is used as the second reagent. 

The reactions of crotyl halides with ethyl ethanoate in the same solvents (mixtures) also gave excellent yields, as can be concluded from the results presented in Table 2.12. 

Table 2.12. Yields of different tertiary homoallylic alcohols from Barbier reactions of crotyl halides, magnesium and ethyl ethanoate in several different solvents and solvent mixtures [53]...

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