Allyl rearrangement tertiary halides

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. 

Cooper(I) carboxylates give esters with primary (including neopentyl without rearrangement), secondary, and tertiary alkyl, allylic, and vinylic halides. A simple Sn mechanism is obviously precluded in this case. Vinylic halides can be converted to vinylic acetates by treatment with sodium acetate if palladium(II) chloride is present. ... 

The present procedure is representative of a fairly general method of converting alcohols to chlorides using carbon tetrachloride and a tertiary phosphine. The reaction occurs under mild, essentially neutral conditions and, as illustrated by the present synthesis, may be employed to convert allylic alcohols to the corresponding halide without allylic rearrangement. 

The transformation of an allylic alcohol to an allylic halide (equation 5) or the reverse reaction normally leads to a mixture of isomers of direct and allylic substitution products. Only when tertiary allylic alcohols are employed or a rearrangement leads to extended conjugation of double bonds does a transposition of functionality occur predominantly While a number of procedures have been developed for the conversion of allylic alcohols to halides without rearrangement, there seems to be only one reaction where a cleanly rearranged product is obtainable in a substitution of a primary or secondary allylic (and propargylic) hydroxy group to a chloride, that is by thionyl chloride in ether, probably by a cyclic SNi process. The regioselectivity is worse in other solvents and is lost in the presence of a base. In accordance with the mechanism it is a syn facial substitution, as has been demonstrated in cyclic cases (equa-... 

Secondary and tertiary alkyl halides give olefins on occasions,223 and / -un-saturated alkyl halides give products of allylic rearrangement.224 -Dibromo-alkanes give bisphosphonium salts in satisfactory to high yield.225 Unlike di-bromomethane, tribromomethane reacts with triphenylphosphine only to the monoquaternary salt stage, the reaction being radical jin nature.226... 

With secondary and tertiary allylic halides or under solvolysis conditions, 8 1 reactions can compete with 8 2, and a mixture of direct displacement and allylic rearrangement products results. 

Retinyl halides are very unstable compounds. The tertiary alcohol (594) underwent an allyl rearrangement reaction with phosphorus tribromide or phosphorus trichloride at low temperatures to give the halide (595) (Surmatis and Thommen, 1969). 

Selective reduction of t-alkyl halides. The ate complex of B-butyl-9-BBN with n-BuLi selectively reduces tertiary alkyl halides to hydrocarbons in high yield without effect on primary or secondary halides. It does not reduce aryl or vinyl halfdes, but does reduce benzyl and allyl halides. The reduction involves a carbonium ion, and thus can proceed with Wagner-Meerwein rearrangements in certain systems. 

N-Alkylation—Secondary Mannich bases can give the corresponding tertiary derivatives by treatment with particular alkylation agents, such as epoxides (affording P-ami-noalcohols) and acrylic derivatives. Tertiary Mannich bases, mostly, are submitted to N-alkylation in order to produce stable quaternary ammonium salts to be subsequently subjected to deamination (Sec. A.2). However, different quaternary ammonium byproducts can be readily given by the reaction. " For instance, a base-catalyzed rearrangement is afforded by allyl ammonium salts 365 (Fig. 144), obtained by N-alkylation of acetylenic Mannich bases with ally] halides. " In the presence of sodium hydride, the compounds 365 yield a wide range of 3-amino-5-hexen-l-yne derivatives 366. 

Base-induced S-allylation of dithioesters [17,18], thionoselenoesters [19] as well as tertiary thioamides [20-23] with allylic halides and alcohols [24] have been commonly used to generate S-allyl ketene-S,W-acetals (W = S,Se, N), which are prone for a thio-Claisen rearrangement. In fact, the marked trend of the starting thiocarbonyl compounds to render the cis-... 

Insertions of vinylic palladium halides with olefins not conjugated with carbonyl groups is more complex. Rearrangement of the initial insertion product to a i-allyl-palladium derivative usually occurs as in Eq. (p). Since the a -allylic complexes are relatively stable, catalytic reactions to form dienes with tertiary amines as bases are slow and inefficient . A useful catalytic reaction occurs, however, if a nucleophilic secondary amine is used as base instead of the tertiary amine. The a-allylic palladium intermediates are attacked by the amine to form tertiary allylic amines and regenerate the catalyst ... 

Examples of the high reactivity of benzylic halides and of allylic halides have been reported. In the latter case, the well established S V rearrangement occurs when a secondary or tertiary allyl halide is used, and this leads to the same products as are obtained from the isomeric primary halide (equation 20), Surprisingly, 3-phenylprop-2-enyl halides afford only low yields in sluggish reactions ". ... 

Thioamides exhibit a nucleophilic character that allows a reversed order of the two deprotonation and alkylation steps (Scheme 9.9). Addition of allyl halides to thioamides provided S-allyl thioimidate salts. Subsequent deprotonation by a variety of bases (notably t-BuOK or simple tertiary amines) led to transient keteneami-nothiocetals, which underwent in situ rearrangement to the awaited y-unsaturated thioamides [51-54]. 

---