Hexadehydro-Diels–Alder (HDDA)-Enabled Carbazolyne Chemistry: Single Step, de Novo Construction of the Pyranocarbazole Core of Alkaloids of the Murraya koenigii (Curry Tree) Family

Abstract

Here we report the use of the hexadehydro-Diels–Alder (HDDA) reaction for the de novo construction of a benzenoid ring in fused polycyclic heteroaromatic carbazole (i.e., [2,3]-benzoindole) skeletons. The strategy allows creation of highly substituted benzenoids. We also describe the HDDA-enabled chemical synthesis of the natural product alkaloids mahanimbine and koenidine. Trapping of the intermediate carbazolyne with a conjugated enal–proceeding through formal [2+2] cycloaddition, 4π-electrocyclic ring-opening, and 6π-electrocyclic ring-closing events—constitutes a robust method for producing pyranocarbazoles.

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

“…Scheme 2 shows the sequence of procedures involved in the formation of Caryl–S(Se)–Caryl and C–C bonds containing benzyne cycloaddition and an intramolecular C–H migration cascade. Aryne intermediate A, which is generated via the HDDA reaction of tetrayne 1, subsequently reacts with the negative selenium ion at the acetylene carbon atoms with small steric hindrance via a nucleophilic addition reaction producing a P-Se four-membered ring intermediate B (Wang and Hoye, 2016; Gupta et al, 2018). Intermediate B is converted to intermediate C via a 4π-electrocyclic ring-opening reaction involving the breaking of P–Se bonds (Kashiki et al, 2009; Yoshioka et al, 2011).…”

Cyclization and Cycloisomerization of π-Tethered Ynamides: An Expedient Synthetic Method to Construct Carbo- and Heterocycles

“…tives. 49 The transformation involves a sequential [4+2] cycloisomerization between 1,3-diynes and the diynophile (yne moiety) to form a benzyne species 144′ in situ, followed by trapping of a nucleophile. This process finally led to the highly functionalized carbazole derivatives 145.…”

Efficient synthesis of polyfunctionalized carbazoles and pyrrolo[3,4-c]carbazoles via domino Diels–Alder reaction

“…Because indoles are readily available materials, the direct extension of indoles to carbazole skeletons has a great advantage [19][20][21][22][23][24][25][26][27]. Therefore, the Diels-Alder reaction of activated 2-vinylindolines or 3-vinylindolines with diverse dienophiles has become the most attractive strategy for the synthesis of carbazole deriv- atives [28][29][30][31][32][33][34][35][36][37][38][39][40]. In recent years, by using the one-pot domino synthetic strategy of in situ-generated 2-vinyl-or 3-vinylindolines and sequential Diels-Alder reaction with activated dienophiles, we have successfully developed several efficient synthetic protocols for diversely functionalized tetrahydrocarbazoles and the corresponding carbazole derivatives [41][42][43][44][45][46][47].…”