A catalytic highly enantioselective allene approach to oxazolines

Abstract

A completely different approach for the asymmetric construction of oxazoline derivatives with an excellent enantioselectivity via the palladium-catalyzed coupling-cyclization of N-(buta-2,3-dienyl)amides with aryl iodides has been reported.

Kinetic Resolution of 2‐N‐Acylamido Tertiary Allylic Alcohols: Asymmetric Synthesis of Oxazolines

“…The bulky 1‐adamantanyl group was amenable substituent, giving s ‐factor of 65 ( 3 s ). The less bulky alkyl substituted 2‐oxazolines were relatively challenging products for asymmetric catalytic synthesis according to previous reports [20m,n] . Encouragingly, kinetic resolution of a secondary alkylacyl substituted 2‐amido allylic alcohols under the standard conditions proceeded smoothly to give the product 4 t with 90% ee and recovered SM with 85% ee.…”

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

“…Thus, yields and scope were first improved by changing the original CuBr/propylamine pair for CuI/cyclohexylamine toward the optimized synthesis of terminal allenes 2 . This methodology was successfully applied for the preparation of different allenols, such as β- or γ-allenols, normally showing low yields under original Crabbé’s reaction conditions (Scheme , reaction a). − To extend the reaction to normal aldehydes, the same research group assumed that finding the proper metal salt/secondary amine combination should be the key for the direct allenylation. Fortunately, diverse matching combination such as ZnI 2 /morpholine or CuI/Bu 2 NH gave successful results from different starting materials (Scheme , reaction b); 1,3-disubstituted allenols 3 were therefore accessible. , Further extension to trisubstituted allenols 4 was achieved by reaction with ketones using CdI 2 /pyrrolidine or the less toxic CuBr-ZnBr 2 /pyrrolidine reagent combination in a sequential addition procedure, or CuBr-ZnBr 2 –Ti­(OEt) 4 /pyrrolidine in the one pot version (Scheme , reaction c). − …”

A Facile Microwave-Assisted Synthesis of Oxazoles and Diastereoselective Oxazolines Using Aryl-Aldehydes, p-Toluenesulfonylmethyl Isocyanide under Controlled Basic Conditions

“…In 2020, Nagib and his group have established a radical cascade strategy for the synthesis of oxazoles via the tandem hydrogen atom transfer (HAT) approach (Scheme G) . In 2018, Ma et al described a highly effective enantioselective synthesis of asymmetric oxazoline derivatives via palladium-catalyzed reaction of aryl or 1-alkenyl iodides with N -(buta-2,3-dienyl) amides (Scheme H) …”

“…30 In 2018, Ma et al described a highly effective enantioselective synthesis of asymmetric oxazoline derivatives via palladium-catalyzed reaction of aryl or 1-alkenyl iodides with N-(buta-2,3-dienyl) amides (Scheme 1H). 31 However, all these methods suffer a few drawbacks such as the usage of toxic Lewis acid, transition-metal catalysts, longer reaction time, and toxic organic solvents such as CH 3 OH, CH 3 CN, and THF . 32−39 Henceforth, there is substantial attention in the improvement of alternate methodologies evading the usage of expensive base catalysts, toxic organic solvents, and transition-metal catalysts.…”