4,5‐Dihydroisoxazoles from Cyclopropyl Ketone Oximes

Abstract

a), 79101-88-5; (26). 79101-89-6; ( 2~) . 79101-90-9; (2d). 79101-91-0; (Ze), 79101-92-1; (312). 79101-93-2; (3b). 79101-94-3; ( 3 4 79101-95-4; (3d). 79101-96-5; (3e). 79101-97-6; (4a). 79101-98-7; (461, 79101-99-8; (4c), 79102-00-4; (4d). 79102-01-5; (4e), 79102-02-6; N-methylsulfamic acid, 41 12-03-2; N-ethylsulfamic acid, 4626-94-2; N-benzylsulfamic acid, 461 19-69-1 [I] a) Review: A.

Accessing Dihydro-1,2-oxazine via Cloke–Wilson-Type Annulation of Cyclopropyl Carbonyls: Application toward the Diastereoselective Synthesis of Pyrrolo[1,2-b][1,2]oxazine

“…The probable mechanistic pathway that this process follows is in agreement with the general reactivity of its precursors, ,, involving condensation of the ACC ( 1 ) with the hydroxylamine- O -sulfonic acid ( 2′ ) and formation of cyclopropyl oxime- O -sulfonic acid ( A , Scheme ). Here, the iminium ion formation and subsequent activation of the cyclopropane ring are attributable to the presence of an acidic proton in the substrate 2′, and thus, no additional activator or reagent is required.…”

“…Most of the reports on the synthesis of 5,6-dihydro-4 H -1,2-oxazine are based on [4 + 2] cycloaddition of nitrosoalkenes to olefins and intramolecular cyclization of the γ-functionalized oxime derivatives (Scheme A), most of which require harsh reaction conditions and sensitive reaction setups. , Surprisingly, the involvement of strain-driven reactivity of donor–acceptor cyclopropanes for the facile synthesis of six-membered oxime ethers has been overlooked for years. The only report considering the intramolecular cyclopropane ring opening by the oxygen atom of the oximino group was back in 1981 by Rentzea using cyclopropyl styryl ketone and hydroxylammonium chloride in constructing 3-vinyl-substituted dihydrooxazines (Scheme A) . However, the strategy suffered low yields (29–50%) even under reflux conditions.…”

Asymmetric Aldol Reaction of α‐Acetoxyimino Aldehydes and its Application in the Synthesis of Substituted 1,2‐Oxazine Derivatives

“…Other synthetic approaches to 1,2-oxazines rely on Lewis acid-catalyzed cyclization of allene-substituted oxime [24] and acid-catalyzed cyclization of cyclopropyloxime. [25] As for the synthesis of chiral 1,2-oxazines, the aldol/Michael reaction, [26] a-aminoxyla- [b] anti:syn [c] ee [a] Unless noted otherwise, reaction was performed by employing 2-acetoxyimino-3-phenylpropanal (0.4 mmol), aldehyde (0.6 mmol), l-proline (0.12 mmol) in DMF (0.4 mL) at À20 8C for the indicated time. After completion of reaction, the aldol product was isolated.…”