(3 + 3) Cycloaddition of Oxyallyl Cations with Nitrones: Diastereoselective Access to 1,2-Oxazinanes

Abstract

Oxyallyl cations are prepared in situ from readily available α-tosyloxy ketones and act as transient electrophilic partners in (3 + 3) cycloaddition with nitrones. Under mild conditions, this method provides a chemoselective and diastereoselective route to polysubstituted 1,2-oxazinanes. A stepwise process is proposed to rationalize the diastereoselectivity of this transformation.

Hydroxy(tosyloxy)iodobenzene (HTIB): A Convenient Oxidizing Agent for the Synthesis of Heterocycles

“…Recently, Cordier and Archambeau introduced a diastereoselective and highly chemoselective approach to synthesize polysubstituted 1,2‐oxazinanes heterocycles 92 via cycloaddition of oxyallyl cationic intermediate 91 , which were produced in situ from α‐tosyloxy ketones 89 with a wide range of nitrones 90 under milder conditions with 58 to 93 % yields (Scheme 32). [73] …”

s-Tetrazine: Robust and Green Photoorganocatalyst for Aerobic Oxidation of N,N-Disubstituted Hydroxylamines to Nitrones

“…To demonstrate the applicability of this photocatalytic oxidative reaction, we were interested to explore the feasibility of developing oxidative 1,3-dipolar (3+3) cycloaddition between N,N-disubstituted hydroxylamines 2 and oxy-allyl cations. In 2018, Archambeau 15 and Rawal 16 groups independently reported an efficient (3+3) cycloaddition of nitrones and -tosyl ketones as stable precursors of oxyallyl cations. Given that cycloadditions were carried out in presence of a base and protic solvents, we reasoned that this reaction could be compatible with our photooxidative process.…”

Ascending of Cycloaddition Strategy for N–O Heterocycles

“…scaffolds (Scheme 16a). 34 Here oxyallyl cation serves as an alleged intermediate, generating from the α-tosyloxy ketones in the presence of hydrogen bond donor TFE solvent. When cyclic ketonitrones were used, spirocyclic products were obtained as a single cis-diastereomer with excellent yields.…”

“…Archambeau and Cordier identified α-tosyloxy ketones as a transient electrophilic 3C synthon that reacts readily with nitrones in 2,2,2-trifluoroethanol (TFE) solvent to give stereodefined 1,2-oxazinane scaffolds (Scheme 16a ). 34 Here the oxyallyl cation is a proposed intermediate, generated from the α-tosyloxy ketone in the presence of the hydrogen bond donor TFE solvent. The use of cyclic ketonitrones with 2-(tosyloxy)pentan-3-one gave spirocyclic products as a single cis -diastereomer with excellent yields.…”