Heteroatom assisted Beckmann fragmentation: towards the synthesis of (±) modhephene

Neighboring‐Group Participation in Nitrile‐Forming Beckmann Fragmentation Reactions: Synthesis of Enantiopure (E)‐2,3‐Di‐O‐substituted‐5‐methoxy‐ pent‐4‐enenitriles and Their Conversion into Pyranosylamines

“…[24] Scheme 1. Reagents and conditions: a) PDC, CH 3 Surprisingly, we observed a very fast reaction (15 min) leading directly to the regioselective formation of (E,2R,3R)-2,3-bis(benzyloxy)-5-methoxypent-4-enenitrile (4a) and (E,2S,3R)-2,3-bis(benzyloxy)-5-methoxypent-4-enenitrile (4b) as the only reaction products and in acceptable yields (60Ϫ70%). The structures of 4a and 4b were determined by HRMS analysis and from the spectroscopic data: 4a, 13 C NMR: δ ϭ 116.6 (CN), 72.5, 69.8 (CH 2 Ph) ppm; 4b, 13 C NMR: δ ϭ 116.8 (CN), 72.3, 69.7 (CH 2 Ph) ppm.…”

Syntheses and Applications of Functionalized Bicyclo[3.2.1]octanes: Thirteen Years of Progress

“…216b In a related tetracyclic complex system, Laxmisha and Rao reported an original heteroatom-assisted Beckmann fragmentation of the keto oxime 506 mediated by triflic anhydride to afford the tricyclo[4.3.3.0 1,6 ]dodecane compound 507 bearing two fused five-membered rings in good yield (Scheme 168). 130 The group of Ogasawara has reported a series of interesting transformations for the preparation of optically active cyclopentanoids from enantiomerically enriched bicyclo[3.2.1]-octanes. 273 For example, on treatment with m-CPBA, 508 furnished regioselectively the lactone 509 together with a minor amount of the regioisomeric lactone (Scheme 169).…”

“…Radical-Based CyclizationsRadical cyclizations of cyclohexane derivatives is a frequently encountered strategy to synthesize bicyclo[3.2.1]octane derivatives, as exemplified in several total syntheses of platensimycin 7 and a recent synthetic approach of pierisformaside C.128 In a study on radical cyclizations of cyclic enynes, Toyota, Yokota, and Ihara reported the regiocontrolled formation of the bicyclo[3.2.1]octane derivative 234 from enyne 233 by a selective 5-exo-dig cyclization process (Scheme 80).129 The compound 234 was then transformed into an advanced known intermediate in the total synthesis gibberellin A 12 . Laxmisha and Rao reported a related tin hydride-mediated 5-exo-dig cyclization 130. In the course of a synthetic study toward polyquinane terpenoids, Biju and Rao reported the 5-exo-trig allyl radical cyclization of the bromo enone 235 (already containing a bicyclo[3.2.1]octane ring system) with trin-butyltin hydride under the standard reaction conditions to afford the tricyclic product 236 containing two distinct interlinked bicyclo[3.2.1]octane moieties.…”

C‐C‐Fragmentierung: Herkunft und jüngste Anwendungen

“…Ähnlich wie in der ursprünglichen Arbeit zu Morphin36 beschrieb Subba Rao eine effiziente heteroatomvermittelte Beckmann‐Fragmentierung von 146 , die das [4.3.3]Propellan‐Derivat 147 lieferte (Schema ) 100. Dieses Produkt ist ein potenzielles Intermediat auf dem Weg zu natürlichen [3.3.3]Propellanen wie Modhephen ( 148 ).…”