Science of Synthesis

Parrain, J.-L.; Thibonnet, J., Science of Synthesis, (2005) 26, 791.

Owing to the poor acidity of the proton of an acetal function and unlike their oxathiane or dithiane analogues, (1,1-dialkoxyalkyl)lithium reagents cannot be prepared by a metalation reaction with simple organolithium reagents. However, these formyl anion equivalents can be efficiently generated from the corresponding trialkyltin precursors. In this context, diethoxymethyllithium appears as a choice reagent in the synthesis of α-oxo acetals ‌135‌ (‌Scheme 61‌). Tributyl(diethoxymethyl)stannane (‌134‌) and tributyl(dimethoxy­methyl)stannane have been converted into the corresponding dialkoxymethyllithium reagents upon transmetalation by butyllithium in tetrahydrofuran.[‌271‌] The temperature appears to be the key parameter controlling the decomposition of diethoxy- or dimethoxymethyllithium into a carbene species. Inside the reactor there is a borderline temperature that allows trapping experiments with electrophiles before decomposition. Nucleophilic additions to esters lead mainly to α-oxo acetals ‌135‌, while additions to acyl chlorides give the double alkylation adducts. Furthermore, more stable dialkoxymethyllithium compounds can be prepared by an identical reaction from 2-(tributylstannyl)-1,3-dioxane.[‌272‌]

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