AbstractKetone‐derived enol borates, especially those having a 4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane unit, are stable compounds, which have been prepared either by borylation of lithium enolates or by oxidation of vinylboronates. TheseE‐ orZ‐enol borates add to aldehydes in a stereoconvergent reaction leading tosyn‐aldols. Aldehyde‐derived enol borates have a high tendency towards polymerization. Their in‐situ addition to aldehydes generates 4‐alkoxy‐1,3,2‐dioxaborinanes, which are inte