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Enantioselective ketone reductions convert prochiral ketones into chiral, non-racemic alcohols and are used heavily for the synthesis of stereodefined alcohols. [ 1 ] Carbonyl reduction, the net addition of H 2 across a carbon-oxygen double bond, is an important way to prepare alcohols.
Partial reduction of acid chlorides to give the corresponding aldehyde product cannot proceed via LAH, since the latter reduces all the way to the primary alcohol. Instead, the milder lithium tri- tert -butoxyaluminum hydride , which reacts significantly faster with the acid chloride than with the aldehyde, must be used.
The Luche reduction can be conducted chemoselectively toward ketone in the presence of aldehydes or towards α,β-unsaturated ketones in the presence of a non-conjugated ketone. [5] An enone forms an allylic alcohol in a 1,2-addition, and the competing conjugate 1,4-addition is suppressed.
When an α,β-unsaturated carbonyl is reduced, three products can result: an allyl alcohol from simple carbonyl reduction, a saturated ketone or aldehyde resulting from 1,4‑reduction (also called conjugate reduction), or the saturated alcohol from double reduction. [19] Use of NaBH 4 can give any of these results, but InCl 3 or NiCl 2 ...
McMurry and Fleming coupled retinal to give carotene using a mixture of titanium trichloride and lithium aluminium hydride. Other symmetrical alkenes were prepared similarly, e.g. from dihydrocivetone , adamantanone and benzophenone (the latter yielding tetraphenylethylene).
The use of an intramolecular MPV reduction can give good enantiopurity. [9] By tethering the ketone to the hydride source only one transition state is possible (Figure 4) leading to the asymmetric reduction. This method, however, has the ability to undergo the reverse Oppenauer oxidation due to the proximity of the two reagents. Thus the ...
The selectivity of this reagent is illustrated by its reduction of all three methylcyclohexanones to the less stable methylcyclohexanols in >98% yield. Under certain conditions, L-selectride can selectively reduce enones by conjugate addition of hydride, owing to the greater steric hindrance the bulky hydride reagent experiences at the carbonyl ...
Nahm and Weinreb also reported the synthesis of aldehydes by reduction of the amide with an excess of lithium aluminum hydride (see amide reduction). The Weinreb–Nahm ketone synthesis. The major advantage of this method over addition of organometallic reagents to more typical acyl compounds is that it avoids the common problem of over-addition.