Diastereoselective and Enantioselective Formal [4+1] Ylide Annulation Leading to Optically Active Isoxazoline N‐Oxides

Abstract

A diastereoselective and enantioselective formal [4+1] ylide annulation of chiral sulfonium salts with various substituted α‐substituted nitroalkene leading to optically active isoxazoline N‐oxides using CF3SO3− as a key anion has been explored. The salient features of this methodology include high diastereo‐ and enantioselecties, easily available starting materials, mild reaction conditions, simple procedure, broad substrate scope and the isoxazoline N‐oxides are conveniently transformed into other functionalized compounds.

Synthesis of 3‐Haloisoxazolines by Deoxygenation of 3‐Haloisoxazoline N‐Oxides under Treatment with Acetyl Bromide

“…The overall sequence involves two steps: [4+1]‐annulation of halonitroalkenes 1 and subsequent deoxygenation of isoxazoline N ‐oxides 2 (Scheme 1, (3)). First of them has already demonstrated its applicability affording good yields of target N ‐oxides 2 [9a,c] . In the present paper we disclose successful reduction (deoxygenation) of products 2 under the acylation conditions.…”

Regio- and diastereoselective access to densely functionalized ketonesviathe Boekelheide rearrangement of isoxazolineN-oxides

“…For a variation of the “formal carbonyl component” in the structure of these aldols, aryl-substituted ylides derived from sulfonium salts 11 were used instead of ester-stabilized ylide 2 (Scheme 4, part A). Since the reaction of nitroalkenes with this type of unstabilized ylides is poorly explored, 9 a short optimization of the conditions was performed using nitrostyrene 1a and benzylsulfonium salt 11a as the model reactants (Ar 2 = Ph, see the ESI†). The highest yield of isoxazoline N -oxide 12a (63%) was achieved when the reaction was conducted in a biphasic system of CH 2 Cl 2 /50% aqueous NaOH with a phase-transfer catalyst (Bu 4 NHSO 4 ).…”

Developments and applications of α-bromonitrostyrenes in organic syntheses

“…A new class of cyclopenta In the same year, the Xie group designed a (4 + 1) ylide annulation between chiral sulfonium salts 63 and 65 with abromonitroalkenes 1 access to enantioenriched isoxazoline Noxides 64 and 66 (Scheme 29). 58 Two types of chiral sulfonium salts, such as a-benzoyl sulfonium triate salts 63 and a-benzyl sulfonium triate salts 65 could smoothly generate the sulfonium ylide intermediates, which served as C1 synthon in (4 + 1)annulation with bromonitroalkene as a 4-atomic synthon. All products were obtained in high yields with excellent enantioand diastereoselectivity.…”