[59648-89-4] · C4H7LiO2 · 1,2-Dimethoxyvinyllithium · (MW 94.04)
(reacts with aldehydes and ketones to form allylic alcohols;1 the functionally equivalent reagent, 2-lithio-1,4-dioxene, reacts with aldehydes, ketones, and methyl halides2,3 to form allylic alcohols and methylated alkenes)
Form Supplied in: prepared in situ and used directly.
Preparative Method: prepared in situ under nitrogen by the reaction of 1,2-dimethoxyvinyl bromide in anhydrous ether at -70 °C with n-Butyllithium in hexane. 1,2-Dimethoxyvinyl bromide is obtained from the reaction at 0 °C of aqueous Glyoxal in methanol (2 equiv)/dichloromethane with Hydrogen Bromide gas, followed by dehydrohalogenation with sodium t-butoxide (1 equiv).1
Handling, Storage, and Precautions: must be prepared and transferred under inert gas (N2 or Ar) to exclude oxygen and moisture.
1,2-Dimethoxyvinyllithium adds to aldehydes and ketones to yield allylic alcohols. The alcohols, when dissolved in THF and 6 N hydrochloric acid, rearrange to a-methoxy-a,b-unsaturated aldehydes.1 With aromatic aldehydes, a-methoxycinnamaldehydes are obtained in isolated yields of 51-76% (eq 1). Cyclohexanone is converted to the unsaturated aldehyde in 86% yield (eq 2).
Pentacarbonyl [(Z)-1,2-dimethoxyvinyl]carbene complexes can be prepared by the addition of the reagent to Hexacarbonylchromium and Hexacarbonyltungsten followed by protonation or alkylation, respectively.4 Synthesis of simple aldehydes from 1,2-dimethoxyvinyllithium and trialkylboranes has been reported.5
2-Lithio-1,4-dioxene is prepared by the addition of n-Butyllithium in hexane to 1,4-dioxene cooled in an ice/water bath2 or by the addition of t-Butyllithium to the dioxene.2,3 The reagent has been identified by its 13C NMR spectrum2 and is stable even at rt. Addition of the reagent to aldehydes and ketones yields secondary and tertiary allylic alcohols (eq 3), which can be converted into a-hydroxy ketones,3 a,a´-dihydroxy ketones,3 and 2-oxaalkanal 1-dithioacetals.5 2-Lithio-1,4-dioxene may also be methylated.2
4-Lithio-2,2-dimethyl-1,3-dioxole, prepared as in eq 4, reacts with aldehydes and ketones to form allylic alcohols, which subsequently afford a-keto aldehydes.6,7
John F. Sebastian
Miami University, Oxford, OH, USA