Allyl chloride rearrangements

Compound 1, 2,2-diniethyl-4-pentenal, has been prepared by the Claisen rearrangement route described above and by reaction of isobutyraldehyde with allyl chloride in the presence of aqueous sodium hydroxide and a phase-transfer catalyst. Both routes are applicable to the synthesis of a variety of substituted 4-pentenals. 

Allyl Halides. Reduction of a polyfunctional allyl chloride occurs without rearrangement and without reduction of the tosylate using Ph2SiH2/ZnCl2/... 

Initial attempts at preparing y,y-disubstituted allyl chlorides employing thionyl chloride in the presence of tributylamine5 led to appreciable amounts of rearranged (tertiary) halides. 

Allylic systems have also provided fertile ground for investigation of ion-pair phenomena. Young, Winstein, and Goering established the importance of ion pairs in solvolysis of these compounds. They showed that ion pairs are responsible for the rearrangement of a,a-dimethylallyl chloride to y,y-dimethyl-allyl chloride (Equation 5.8).24 Goering s labeling methods have subsequently supplied a number of details about allylic ion-pair structure.25... 

Allyl chloride or polychlorinated ethanes with a cleavable C-Cl bond were also investigated thermally (250-290 °C) by Haszeldine et al. [267]. Beside normal and reverse monoadducts produced in poor yields, cyclic or thermal rearranged compounds were obtained. 

Notice that these reactions take place with allylic chlorides. We should not expect an alkyl chloride to be particularly good at Sn2 reactions as chloride ion is only a moderate leaving group and we should normally prefer alkyl bromides or iodides. AUylic chlorides are more reactive because of the alkene. Even if the reaction occurs by a simple Sn2 mechanism without rearrangement, the alkene is still making the molecule more electrophilic. 

If our proposal that allylic sulfoxides rearrange reversibly to sulfenate esters is correct, then, if we make the sulfenate ester by another route, it too should rearrange to an allylic sulfoxide—and indeed it does. The sulfenate ester arising from reaction of allylic alcohols with PhSCl (phenylsulfenyl chloride) cannot be isolated instead, the allylic sulfoxide is obtained, usually in very good yield, and this method is often used to make allylic sulfoxides. 

For allyl ethers, rearrangement of the double bond to the more thermodynamically stable enol ether can be accomplished using trisjtriphenylphosphinejrho-dium(l) chloride (Wilkinson s catalyst). A possible mechanism for the rhodium(l)-... 

Chloriuatton of alkenes, Allylic chlorination is usually conducted by a free-radical reaction with NCS. Chlorination can be effected with catalysis by C6H5SeCl, in which case the main product is usually the rearranged allylic chloride. However, the formation of rearranged allylic chloride is sensitive to the structure of the alkenes and also to the particular selenium compound used as catalyst. See also N-phenylselenosuccinimide, this volume. 

AllyUc chlorination. /0-Pinene reacts with 2 to afford selenide 3 in excellent yield. When 3 is treated with NCS, the rearranged allylic chloride 4 informed as the principal product. The latter reaction is general for allylic selenides. An analogous reaction of 3 with chloramine-T effects allylic amination to 6 (44% yield). The... 

---