Festkörperreduktion von Ketonen mit NaBH₄

Abstract

Ohne Lösungsmittel, lediglich durch Verreiben der festen Reaktanten in einem Mörser, konnten nicht nur einfache Ketone mit NaBH4 reduziert werden, es gelangen auch regio‐ und enantioselektive Reduktionen, wenn Einschlußkomplexe verwendet wurden. Aus den Ketonen 1 und 3 wurden die als Synthesebausteine interessanten Hydroxyketone 2 bzw. 4 hergestellt.

Sodium Tetraalkoxyborates: Intermediates for the Quantitative Reduction of Aldehydes and Ketones to Alcohols through Ball Milling with NaBH4

“…The reduction of aldehydes and ketones with an excess amount of NaBH 4 (2) in solution usually gives the corresponding alcohols together with much waste, also from further auxiliaries, [5][6][7] even though aqueous media appeared attractive. [1,2] Therefore, the quantitative hydrolysis of the now easily available pure tetraalkoxyborates 3 under very mild conditions by simple addition of water is rewarding.…”

“…[3,4] There are also reports for the reduction of aldehydes and ketones with NaBH 4 under solvent-free conditions. [5] However, most of them have disadvantages for practical utility including excessive amounts of reducing agent, addition of catalysts, long reaction times, and the necessity of chromatographic workup. For example, benzophenone and a 10-fold molar amount of sodium borohydride were kept in a dry box at room temperature with occasional co-grinding of the reactants in an agate mortar with pestle for 5 d.…”

TADDOLs, Their Derivatives, and TADDOL Analogues: Versatile Chiral Auxiliaries

“…[170,171] Although regioselective [172] and diastereoselective [173,174] transformations have also been observed in TADDOL host ± guest compounds, we limit our discussion here to enantioselective transformations, especially photochemical reactions.…”

TADDOLe, ihre Derivate und Analoga – vielseitige chirale Hilfsstoffe

“…[170,171] Obwohl in TADDOL-Festkˆrpern auch regioselektive [172] und diastereoselektive [173,174] Transformationen beobachtet wurden, soll hier nur auf die enantioselektiven, vor allem photochemischen Umwandlungen eingegangen werden.…”