Synthesis of d‐mannitol‐based crown ethers and their application as catalyst in asymmetric phase transfer reactions

Abstract

A few new d-mannitol-based monoaza-15-crown-5 type chiral lariat ethers and 18-crown-6 type macrocycles were synthesized. These crown compounds were used as phase transfer catalysts in asymmetric Michael addititons and in a Darzens condensation under mild conditions to afford the corresponding products in a few cases in good to excellent enantioselectivities. In the Michael addition of diethyl acetoxymalonate to trans-chalcone, in the addition of diethyl acetamidomalonate to ß-nitrostyrene, in the reaction of diethyl bromomalonate with benzylidene malononitriles, in the cyclopropanation reaction of diethyl bromomalonate and 2-benzylidene-1,3-indandione, and in the Darzens condensation of α-chloroacetophenone with benzaldehyde, maximum enantioselectivities of 39%, 65%, 99%, 56%, and 62%, respectively, were obtained in the presence of the d-mannitol-based macrocycles as the catalysts.

Catalytic Asymmetric Darzens and Aza‐Darzens Reactions for the Synthesis of Chiral Epoxides and Aziridines

“…The same authors accomplished a catalytic asymmetric Darzens condensation of phenacyl chloride and benzaldehyde using D-mannitol-based monoaza-15-crown-5-type chiral ethers 20 j-o ( Figure 1) as PTCs. [29] The highest enantioselectivity (62 % ee) was achieved with catalyst 20 n containing a cyclohexyl substituent. Poor enantioselectivity was observed when analog crown ether 20 o was used, establishing the crucial requisite of a hydroxypropyl side arm for the enhancement of the enantiocontrol of the process.…”

“…Therefore, the substituent at C(1) seems to have no effect in the enantioselectivity of the process. The same authors accomplished a catalytic asymmetric Darzens condensation of phenacyl chloride and benzaldehyde using D‐mannitol‐based monoaza‐15‐crown‐5‐type chiral ethers 20 j – o (Figure ) as PTCs . The highest enantioselectivity (62 % ee ) was achieved with catalyst 20 n containing a cyclohexyl substituent.…”

H2O2 as a green and environmentally benign reagent for the oxidation of Sulfides in the presence of {[K.18-Crown-6]X3}n (X= Br, I) compared with some other organic tribromides

“…As we know, crown ethers are phase transfer catalysts [20], and we expect this catalyst to promote the reaction better than some other organic tribromides. Therefore, we applied some other reported organic tribromide i.e.…”

One Pot and Two Pot Synthetic Strategies and Biological Applications of Epoxy-Chalcones

“…This route required additional step to prepare highly moisture sensitive benzoyl chloride reactant. Darzen reaction was further modified by introducing D-manitol-based crown ether [36], methyl α-d-glucopyranoside [37] and d-glucosebased lariat ethers [38] as catalyst in phase transfer conditions to achieve 78-92% yield of the desired product.…”