Selective Reductions. 59. Effective Intramolecular Asymmetric Reductions of α-, β-, and γ-Keto Acids with Diisopinocampheylborane and Intermolecular Asymmetric Reductions of the Corresponding Esters with B-Chlorodiisopinocampheylborane

Abstract

A comparison of the stereochemistry of the products obtained from the intramolecular asymmetric reduction of a series of keto acids with (-)-diisopinocampheylborane and intermolecular asymmetric reduction of the corresponding series of keto esters with (-)-B-chlorodiisopinocampheylborane ((-)-DIP-Chloride) has been made. The stereochemistry of the hydroxy acids from the reduction of keto acids is dependent only on the enantiomer of the reagent used. The stereochemistry of the products from the reduction of keto esters is also consistent, except those of aliphatic alpha-keto esters. alpha-, beta-, and gamma-keto acids provide the corresponding hydroxy acids in 77-98% ee, and the alpha- and gamma- keto esters afford the hydroxy esters in 82->or=99% ee. beta-Keto esters do not undergo reduction. Although the reduction of delta-keto acids does not proceed under the same reaction conditions, the reduction of delta-keto esters is facile. All of the products from the reduction of gamma-keto acids and esters and delta-keto esters were converted to the corresponding lactones. This study revealed that DIP-Chloride is an efficient reagent for the reduction of alpha-keto esters at low temperatures.

Efficient Hydrogenation of Biomass Oxoacids to Lactones by Using NHC–Iridium Coordination Polymers as Solid Molecular Catalysts

“…In light of highe fficiency of solid molecular catalyst 1a in the reduction of LA to GVL, we sought to furtheri nvestigate its feasibility to catalyze the reduction of variouss ubstituted LAs, LA derivativeso re ven analogues to access an umber of functional lactones ( Table 2). [43,44] When the ketone terminal of LA was substitutedb ya romatic rings, all substrates with different electronic and steric properties were well tolerated (6-9); up to 98 %i solated yield could be obtained in the presence of 0.1 mol %s olid 1a.F or a-OMe-substituted substrate, only am oderate yield (67 %) could be obtained even with an increasedc atalyst loading of 1mol %( 6c), whereas the methyl analogue resulted in 95 %y ield of 6b at 0.1 mol %c atalyst loading. Notably,h alides were compatible and delivered the corresponding lactones (7)i ng ood yields, which may also provide an opportunity for their furthert ransformation.…”

Synthesis of (+)‐Patulolide C Using R‐(+)‐γ‐Valerolactone as a Chiral Synthon.

“…Considering the high stereoselectivity during Wittig reaction of the corresponding lactol of optically pure γ‐valerolactone, the latter becomes a very good chiral synthon in the synthesis of natural products . A variety of methods are in practice for the synthesis of optically pure γ‐lactones that either use stoichiometric or catalytic chiral reagent systems or enzymes as part of a greener approach for the asymmetric hydrogenation of γ‐keto esters. With a lot of progress being made in the field of asymmetric reduction of γ‐keto esters using enzymes it has now become quite facile to obtain the chiral alcohols that afford chirally pure γ‐valerolactones in large quantities starting from γ‐keto esters.…”

Preparation of Enantioenriched γ-Substituted Lactones via Asymmetric Transfer Hydrogenation of β-Azidocyclopropane Carboxylates Using the Ru-TsDPEN Complex

“…It would be very easy to understand here that if the racemic cyclopropane carboxylates were used, the γ-oxo esters would also be efficiently produced. The asymmetric reduction of the γ-oxo esters has been reported with some chiral reagents via stoichiometric processes or catalytic processes with control of the stereochemistry. Thus, if a suitable chiral reductant was applied, further asymmetric reduction of the γ-oxo esters to enantioenriched γ-hydroxybutyrates might be possible.…”