[54780-30-2] · C7H13LiO2 · 2-Lithio-3,3-diethoxy-1-propene · (MW 136.12)
(is able to transfer a masked acrolein unit to various electrophiles such as carbon dioxide,1 aldehydes,2 ketones,2 and amides;3 the corresponding cuprate also allows 1,4-addition to conjugated enones,4 coupling with allylic halides,4b and 1,2-opening of 3,4-epoxycycloalkenes5)
Alternate Names: 3,3-diethoxy-1-propen-2-yllithium; 3,3-diethoxy-2-lithio-1-propene.
Preparative Method: under nitrogen, n-Butyllithium (2 molar in hexane, 0.95 equiv) is slowly added at -70 °C to 2-bromo-3,3-diethoxy-1-propene in dry THF (1.6 mL mmol-1 of bromoacrolein acetal).2d
Handling, Storage, and Precautions: this solution of a vinyllithium should be held under nitrogen at low temperature (the upper limit for the thermal stability has been estimated to be approx. -40 °C), kept out of oxygen and moisture, and used immediately for best results.
Addition of ketones2 or aldehydes2,6 to the title organolithium (1) in THF at -70 °C leads to the corresponding b-hydroxy-a-methylene acetals in respectively 50 and 80% yields (eq 1). 1,2-Addition is also observed with conjugated enones7 or enals. These secondary allylic alcohols can be stereoselectively transformed into trisubstituted functionalized alkenes.2,8
Reaction of (1) with enantiomerically pure 2,3-O-isopropylidene-D-glyceraldehyde gives the diastereoisomer adducts (erythro:threo = 2:1) in 70% yield (eq 2).2c These are precursors of C-2 branched chain pentoses, a-methylenelactones, or 2,4-disubstituted furans.8b,9
The reagent also reacts with other electrophiles such as Carbon Dioxide,1 Chlorotrimethylsilane, and amides3 (eq 3). In the latter case, a-methylene-b-oxoacetals are obtained in about 70% yield, except for R = H or Me (20-30% yield). These adducts lead to substituted b-keto enol ethers by addition of Lithium Dimethylcuprate.10
Synthetic equivalents of 2-lithiopropenal11 and of its diethyl acetal12 (eqs 4 and 5) have also been reported.
(1) can be transformed into other organometallic species such as vinylcopper (2),4b homogeneous diorganocuprates (3),4a and mixed diorganocuprates such as phenylthio-,4b,c alkynyl-,4,5 or cyanocuprate (4)5
The (a-diethoxymethyl)vinylcopper reacts with allylic halides and gives only 1,2-addition reactions with conjugated enones.4b Homogeneous4a,13 and mixed4c diorganocuprates react with a variety of a,b-unsaturated ketones to afford 1,4-adducts in moderate to excellent yields, depending upon steric hindrance in the enone (eq 6). These adducts have been shown to be suitable precursors to a-methylene-g-lactones.4c Mixed diorganocuprates also allow coupling with allylic halides4b and allylic epoxides5 (eqs 7 and 8), but not with vinyl or saturated halides.
Cyclic analogs (5)-(7) of the vinyllithium with a b-acetal function14 have also proved useful in a variety of synthetic schemes.
Acrylate anion analogs such as orthoesters (8)15 and (9)16 and esters (10),17 (11),16 and (12)18 have been described (Table 1). Cuprate (10) reacts with allylic and propargylic halides,17,19 but in contrast to most organocuprate reagents, (10) reacts at low temperature with conjugated enones to yield predominately 1,2-addition products.7,20
Yves Le Merrer & Jean-Claude Depezay
Université René Descartes, Paris, France