Organocatalytic Synthesis of Oxazolines and Dihydrooxazines from Allyl‐Amides: Bypassing the Inherent Regioselectivity of the Cyclization

Abstract

A selective and efficient methodology for the construction of either oxazolines or dihydrooxazines from the corresponding allyl-amides is reported. Bypassing the inherent selectivity of the cyclization and depending on the substitution pattern of the substrate, a selective epoxidation-cyclization was developed leading to either the five-membered or the six-membered ring, upon simple and complementary reaction conditions. The cyclization products were obtained in good to excellent yields and high selectivities.

Organocatalytic activation of hydrogen peroxide: towards green and sustainable oxidations

“…On the contrary, in an acidic environment (TFA), a 6- endo-trig cyclization afforded dihydrooxazines 55 ( Scheme 13D ). 38 An interesting feature is that allylamines show excellent chemoselectivity under the reaction conditions. 38 This unique feature enabled the application of a Meisenheimer rearrangement step towards O -allylhydroxylamines 58 ( Scheme 14 ).…”

Epoxides: Small Rings to Play with under Asymmetric Organocatalysis

“…In 2018, Kokotos developed an organocatalytic methodology for the selective synthesis of racemic oxazolines and dihydrooxazines starting from allyl amides. 111 The regioselectivity of the cyclization, in general, followed Baldwin's empirical rules and depended on the substitution pattern of the substrate. Using simple and complementary reaction conditions, the epoxidation/cyclization sequence allowed the inherent selectivity of cyclization to be overcome, affording either the fivemembered or the six-membered rings.…”

“…In 2018, Kokotos developed an organocatalytic methodology for the selective synthesis of racemic oxazolines and dihydrooxazines starting from allyl amides . The regioselectivity of the cyclization, in general, followed Baldwin’s empirical rules and depended on the substitution pattern of the substrate.…”

Metal-Free Synthesis of 1,3-Disiloxanediols and Aryl Siloxanols

“…Several methods for silane hydrolysis have also been reported using stoichiometric oxidants such as dioxiranes . Recently, an organocatalytic hydrolysis of non-oxygenated silanes with 2,2,2-trifluoroacetophenone (BzCF 3 ) was reported by Kokotos and co-workers, which relies on the in situ formation of a highly active oxidizing species under basic and biphasic conditions. ,− Arzumanyan et al has investigated the hydrolysis of primarily alkyl siloxanes; however, a larger investigation of aryl siloxanes has not been demonstrated . Herein, we present the first examples of organocatalytic and base-catalyzed methods for conversion of hydrido-siloxanes to the corresponding 1,3-disiloxanediols.…”