Homoallylic alcohols, electrosynthesis

The electrosynthesis of homoallyl alcohols (193) or 8-hydroxy esters (196) has been carried out by the reaction of methallyl chloride (190) (Scheme 75) or... 

The Barhier-type reaction of aldehydes and ketones with allyl halides (485) in the presence of Sml2, leading to homoallyl alcohols (486), has received recent interest as a one-step alternative to the Grignard reaction. However, the reactions require the use of stoichiometric amounts of the reducing Sm(III) species. Recently, the electroreductive Barhier-type allylation of carbonyl compounds in an SmH-mediated reaction has been developed [569]. The electrolysis of (485) is carried out in a DMF-SmCl3-(Mg/Ni) system in an undivided cell to give the adduct (486) in 50 85% yields (Scheme 168) [569]. Electrosynthesis of y-butyrolactones has been achieved by the reductive coupling of ethyl 3-chloropropionate with carbonyl compounds in the presence of a catalytic amount of SmCfi [570]. 

Reductions. Sm(II) has been developed as a versatile one-electron reductant of broad utility in organic synthesis. Sm(II) can be prepared and regenerated in situ by reduction of Sm(III) in DMF with a consumable magnesium anode (52-54), Under these conditions aromatic esters are reductively dimerized to 1,2-diJketones with only 10% Sm(III) (52). Similarly, allylic chlorides can be added to ketones to give homoallylic alcohols (55). SmCl3-catalyzed electrosynthesis of y-butyrolactones from 3-chloro esters and ketones or aldehydes proceeds in 25-76% yield (54). 

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