Cationoid complexes as reagents in electrophilic addition reaction

Cyclization of 5-hexynoic acid to 3-alkoxy-2-cyclohexenones

“…We did not observe formation of the alternative 5-membered cyclic product. This result is consistent with those reported by Smit whose acyclic cases led exclusively to acylation at the unsubstituted end of terminal alkynes [ 8 ]. Additionally, the preference for formation of the 6-membered cyclization product is likely biased by geometric factors due to the propylene tether linking the acyl chloride and alkyne moieties.…”

“…Treatment of 5-hexynoic acid with trifluoroacetic anhydride followed by decomposition of the reaction mixture in methanol under reflux yielded 1,3-cyclohexandione in 25% yield. Later, Smit and coworkers reported the closely related acyclic reaction between alkynes and acyl cations leading to β-diketones in 25–76% yield [ 8 – 9 ]. Interestingly, only reactions run in mildly nucleophilic solvents, such as nitromethane, yielded products.…”

“…Building on the work of Tedder [ 7 ] and Smit [ 8 – 9 ] we have improved the alkynoic acid cyclization approach in a manner that allows ready access to 3-alkoxy-2-cyclohexenones in good yields. Further elaboration of this methodology is ongoing.…”

Biomimetic Cyclizations of Functionalized Isoprenoid Polyenes: A Cornucopia of Synthetic Opportunities

“…This result can be explained by assuming that, compared to the 1,5-diene 62, different geometries of the transition state, for example 69a and 69b (Fig. Oxidative decyanation of 71 to ketone 72, followed by demethylation (BBr 3 ) and O 2 oxidation of the crude catechol, delivered antineoplastic agent taxodione (73) in 68% yield from 71 [51] (Scheme 26). Fig.…”

“…They reported the Friedel-Crafts-like reactions of compounds of the type RCOX or MeOCH 2 X (X= BF 4 , SbF 6 , 2,4,6-(NO 2 ) 3 C 6 H 2 SO 3 (TNBS); R= Me, C 2 H 5 , i-C 3 H 7 , terz-C 4 H 9 , C 6 H 5 ) with geranyl deri- vatives (108), methyl geranate (111), and ethyl farnesate (114) [69][70][71][72][73]. They reported the Friedel-Crafts-like reactions of compounds of the type RCOX or MeOCH 2 X (X= BF 4 , SbF 6 , 2,4,6-(NO 2 ) 3 C 6 H 2 SO 3 (TNBS); R= Me, C 2 H 5 , i-C 3 H 7 , terz-C 4 H 9 , C 6 H 5 ) with geranyl deri- vatives (108), methyl geranate (111), and ethyl farnesate (114) [69][70][71][72][73].…”