Asymmetric Synthesis of Iridoid Derivatives Using Resolved 2‐Phenylindoline as a Chiral Auxiliary

Abstract

An asymmetric synthetic route to cis,cis-nepetalactol (component of the sex pheromone for the hop aphid, Phorodon humuli) is presented. 2-Phenylindoline was resolved to provide a chiral auxiliary for the cycloaddition of oxocitral. The resolution was made by chromatographic separation of the diastereomers of the urea derivative made from 2-phenylindoline and with (R)-(+)-α-methylbenzyl isocyanate, followed by reductive cleavage of the isolated diasteromers

The Importance of Organocatalysis (Asymmetric and Non‐Asymmetric) in Agrochemicals

“…[31,7c] The yield of the final cyclization step (36 %, 86 % ee) was lessened due to the the sensitivity of rotundial to degradation. [32] The overall yield of 25 % compares favorably with earlier reported syntheses, [33] and the optical rotation was in agreement with the desired (R)-configuration (Scheme 9).…”

“…The proposed mechanism for desired enantioselective organocatalytic RC‐type cyclization involves the well‐established iminium ion intermediates [30] while using commercially available Jørgensen‐Hayashi catalyst 17 [31,7c] . The yield of the final cyclization step (36 %, 86 % ee) was lessened due to the the sensitivity of rotundial to degradation [32] . The overall yield of 25 % compares favorably with earlier reported syntheses, [33] and the optical rotation was in agreement with the desired ( R )‐configuration (Scheme 9).…”

Chiral Phosphoric Acid-Catalyzed Oxidative Kinetic Resolution of Indolines Based on Transfer Hydrogenation to Imines

“…The use of 1.0 equiv of ketimine 3d , prepared from acetophenone and 3,4,5-trimethoxyaniline, further improved the enantioselectivity to >99% ee with 64% conversion (entry 4). Finally, the optimum reaction conditions were established as follows: 5 mol % ( R )- 1 , ketimine 3d (0.6 equiv), and 5 Å molecular sieves (MS) in benzene at 50 °C (entry 5). , …”

Crossed Intramolecular Rauhut−Currier-Type Reactions via Dienamine Activation

“…Since the Jørgensen−Hayashi catalyst ( IV ) is specific toward aldehydes, selective activation over other Michael acceptors such as α,β-unsaturated ketones might be attainable. More importantly, this mode of activation should allow the activation of β-disubstituted alkenes, thereby providing an entry into the iridoid class , of natural products, found widely in plants and insects which possess important pharmacological activities . We started our investigations using compound 6a as the test substrate in order to explore the viability of an enantioselective cyclization to give cyclopentene 7a .…”