Total Syntheses of Chelidonine and Norchelidonine via an Enamide–Benzyne–[2 + 2] Cycloaddition Cascade

Abstract

Total syntheses of chelidonine and norchelidonine featuring an enamide-benzyne-[2 + 2] cycloaddition initiated cascade is described. The cascade includes a pericyclic ring-opening and intramolecular Diels-Alder reaction.

Alkane desaturation by concerted double hydrogen atom transfer to benzyne

“…Indeed, we can infer that this has already been encountered. Recent reports show THF to be an inferior medium(vs. 1,4-dioxane 24 or diethyl ether 25 ) for some benzyne trapping reactions. This is consistent with (i) the results we reported above for the relative efficiency of THF vs. 1,4-dioxane as a2H-donor (entries 6 vs. 7, tabular inset in Fig.…”

Tertiary Enamides as Versatile and Valuable Substrates to Reach Chemical Diversity

“…This method could be extended to the total syntheses of benzophenanthridine alkaloids chelidonine (17) and norchelidonine (18) (Scheme 3B). 11 In 2013, an interesting strategy for the synthesis of aminocyclobutanes 21 that relies on iron-catalyzed [2+2] cycloaddition between enimides 19 and alkylidene malonates 20 was explored by Waser and co-workers. 12 This method benefits from the use of an inexpensive and non-toxic iron catalyst supported on alumina.…”

Versatile Dibenzothio[seleno]phenes via Hexadehydro-Diels–Alder Domino Cyclization

“…These reactions of tetraynes with triphenylphosphine selenide or triphenylphosphine sulfide produce various fused products in excellent yields without catalysts, oxidants, bases, or metals. This method, with no need for directing groups, however, exhibits excellent regioselectivity and can generate fused 2,3-dihydro-1H-benzoindenoselenophene and 2,3-dihydro-1H-benzoindenothiophene via a one-pot multiterminal HDDA (Ma et al, 2012; Wang et al, 2012; Karmakar et al, 2018) cycloaddition reaction (1a−1q) in excellent yields (Table 1). Consequently, this route could afford an economical, efficient, and direct path of forming highly substituted dibenzoselenophene- and dibenzothiophene-containing compounds.…”