Encyclopedia of Reagents for Organic Synthesis
Acetaldehyde reacts with a myriad of nucleophilic reagents, generally providing excellent yields of the two-carbon extended secondary alcohols. Aryl-,1 alkynyl-,2 and alkyllithiums3 react rapidly with acetaldehyde even at low temperature. A chiral vinyllithium reagent at low temperature reacts stereoselectively to afford a 10:1 mixture of diastereomeric alcohols (eq 1).4 Aryl5 or alkyl6 Grignard reagents behave in an analogous manner with acetaldehyde to give the secondary alcohols or the methyl ketones7 upon subsequent oxidation. Allyl organometallics react with varying degrees of stereocontrol depending on the metal and conditions to give the corresponding homoallylic alcohols.8 Chiral allylboronates also react with acetaldehyde at -78 °C to afford the homoallylic alcohols with high enantioselectivity.9 trans-Epoxides are produced selectively through the Darzens reaction of acetaldehyde with halomethyl sulfones under basic phase transfer conditions.10 Classical Wittig reagents11 and Horner-Emmons phosphonate12 ylides react with acetaldehyde to give the alkene.
Acetaldehyde serves as an electrophilic partner in the aldol condensation with a wide array of enolates.13 Knoevenagel condensation of acetaldehyde with active methylene compounds in the presence of base provides good yields of the ethylidene substituted compounds.14 Addition of two equivalents of an active methylene compound to acetaldehyde results in a Michael addition of the second equivalent to the initially formed ethylidene.15 Tollens reaction of acetaldehyde with formaldehyde gives pentaerythritol.16 The addition of acetaldehyde in a Baylis-Hillman condensation with Ethyl Acrylate using 1,4-Diazabicyclo[2.2.2]octane (DABCO) as catalyst gives a 90% yield of the allylic alcohol.17 The stereoselective aldol reaction of acetaldehyde with achiral18 and chiral19 imide enolates has received much attention and is a proven method for controlling acyclic relative and absolute stereochemistry.13 For example, the boron enolate of a norephedrine-derived propionyloxazolidine reacts with acetaldehyde to afford in 90% yield and >98% de the syn aldol product (eq 2).19a Acetaldehyde also smoothly undergoes nitro-aldol condensation to the corresponding nitro alcohols.20 The lithium enolates of a variety of heterocycles react with acetaldehyde to give good yields of product alcohols.21 In addition, the zinc,22 copper,23 and boron24 enolates of esters and ketones provide aldol products with acetaldehyde.
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