The hydrogen bond directing effect in nitrile oxide cycloadditions to allylic substituted cyclopentenes

Metal-Involving Synthesis and Reactions of Oximes

“…Oxone is required to regenerate the catalytically active ruthenium­(III) from ruthenium­(II). This reaction is an extension of previously known protocol for isoxazoline generation from 261 in the presence of alkene and (NH 4 ) 2 [Ce­(NO 3 ) 6 ] and represents a complex version of more abundant reaction that starts from chloroximes (for recent works see refs and ).…”

1,6-Dioxo-2-azaspiro[3.4]oct-2-enes and Related Spirocycles: Heterocycles from [3 + 2] Nitrile Oxide Cycloadditions with 2-Methyleneoxetanes, -Thietanes, and -Azetidines

“…The contrasteric selectivity observed to form 3ag as the only diastereomer is likely due to additional stabilization from the secondary amine acting as a hydrogen-bond donor with 2a . While postulated in several nitrile oxide cycloadditions, − the solid-state structure of 3ag provides further experimental support to this hypothesis. A weak hydrogen bond between the secondary amine and the isoxazoline oxygen was observed in 3ag [O(1)–H(2) = 2.479 Å, O(1)–N(2) = 2.887(4) Å, O(1)–H(2)–N(2), and ∠O(1)–H(2)–N(2) = 108.9°] and suggests that similar or stronger hydrogen-bonding interactions could be present during the cycloaddition.…”

“…More recent studies by Quadrelli and co-workers have confirmed this effect with an allylic acetamide and demonstrated that it could be somewhat suppressed with solvents capable of hydrogen bonding with the amide. 35 Park and Kurth reported similar stereodirecting effects in nitrile oxide cycloadditions with methylenecyclobutanes possessing homoallylic carbamates. 36,37 Given that our solution conformational analysis strongly supported two distinct major diastereoselectivities depending on the steric profile or the presence of a hydrogen bond donor, we pursued further structural characterization of the novel spirocyclic structure using single-crystal X-ray diffraction.…”

“…While the reaction between benzonitrile oxide and cyclopentene with an allylic OMe resulted in predominantly an anti-facial approach for cycloaddition (>90%), a benzamide at this position gave 90% of a syn-facial approach. More recent studies by Quadrelli and co-workers have confirmed this effect with an allylic acetamide and demonstrated that it could be somewhat suppressed with solvents capable of hydrogen bonding with the amide . Park and Kurth reported similar stereodirecting effects in nitrile oxide cycloadditions with methylenecyclobutanes possessing homoallylic carbamates. , …”