Rearrangements allylic, with Grignard reagents

Primary allylic sulfides of derivatives of benzothiazole-2-thiol react with Grignard reagents in the presence of copper(I) iodide to yield olefins, with or without allylic rearrangement, depending on the nature of the solvent and the allylic sulfide [71 Eq. (62) and Table 14]. 

Reaction with allylic ethers. Alkenes are obtained by reaction of allylic ethers with Grignard reagents catalyzed by cuprous chloride or bromide. Direct replacement of the ether group takes place as the major reaction when the ether is primary. Secondary and tertiary allylic ethers react mainly with rearrangement. 

Treatment of (—)-(S)-276 with allyl Grignard reagents gives optically active allylic sulphoxides 288. This reaction, however, involves an allylic rearrangement via transition state 289 as evidenced by Mislow and his collaborators362 (equation 160). 

Structural rearrangements are not encountered with saturated Grignard reagents, but allylic and homoallylic systems can give products resulting from isomerization. NMR studies indicate that allylmagnesium bromide exists as a CT-bonded structure in which there is rapid equilibration of the two terminal carbons.101 Similarly,... 

The parent compound, 69, has been synthesized and characterised <2003ZFA1475>. 4-Chloro-hepta-l,6-diene was reacted with Mg. No Grignard rearrangement was noticed but instead the Grignard reagent was converted into l-allyl-3-butenylphosphonous dichloride by reaction with PC13. Reduction with LiAlH. produced l-allyl-3-butenyl-phosphane. Radical-initiated cyclization led to the product, l-phosphabicyclo[3.3.0]octane. Four derivatives were similarly prepared and characterized (70-73). Compound 74 was similarly prepared via a radical reaction < 1997PS(123)141 >. 

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