Expedient Route to the Functionalized Calyciphylline A-Type Skeleton via a Michael Addition–RCM Strategy

Enantioselective Total Synthesis of (-)-Himalensine A via a Palladium and 4-Hydroxyproline Co-catalyzed Desymmetrization of Vinyl-bromide-tethered Cyclohexanones

Herein, we describe the convergent enantioselective total synthesis of himalensine A in 18 steps, enabled by a highly enantio- and diastereoselective construction of the morphan core via a palladium/hydroxy proline co-catalyzed desymmetrization of vinyl-bromide-tethered cyclohexanones. The reaction pathway was illuminated by density functional theory calculations, which support an intramolecular Heck reaction of an in situ-generated enamine intermediate, where exquisite enantioselectivity arises from intramolecular carboxylate coordination to the vinyl palladium species in the rate- and enantio-determining carbopalladation steps. The reaction tolerates diverse N-derivatives, all-carbon quaternary centers, and trisubstituted olefins, providing access to molecular scaffolds found in a range of complex natural products. Following large-scale preparation of a key substrate and installation of a β-substituted enone moiety, the rapid construction of himalensine A was achieved using a highly convergent strategy based on an amide coupling/Michael addition/allylation/ring-closing metathesis sequence which allowed the introduction of three of the five rings in only three synthetic steps (after telescoping). Moreover, our strategy provides a new enantioselective access to a known tetracyclic late-stage intermediate that has been used previously in the synthesis of many Daphniphyllum alkaloids.

Synthesis and reactivity of hydroindole enelactams leading to densely functionalized scaffolds

The 5-endo-trig radical cyclization of N-benzyl-N-[(2-substituted)cycloalkenyl] trichloroacetamides (tetrasubstituted enamides) using Bu3SnH and AIBN is a reliable synthetic procedure giving access to 3a-methyl- and 3a-methoxycarbonyl enelactams. The substrate-controlled diastereoselective enolate alkylation of these enelactams resulted in the synthesis of a set of 3-substituted derivatives that upon reduction furnished polyfunctionalized cis-octahydroindoles. The latter building blocks, which embody three consecutive stereocenters at C-3, C-3a, and C-7a, were also synthesized through an initial reductive radical cyclization using (carbo-substituted)dichloroacetamides.

The chemistry of Daphniphyllum alkaloids

The triterpenoids Daphniphyllum alkaloids share the unique fused hexacyclic ring framework are isolated from the genus Daphniphyllum. These natural products possess comprehensive biological activities and exhibit excellent potential medicinal appliment. This review covers the reported isolation studies and biological activities of Daphniphyllum alkaloids spanning the period from 1966 to the beginning of 2020, In the meantime, the total synthesis of Daphniphyllum alkaloids will be emphatically summarized for supplement over this review series.

Regioselective and diastereodivergent organocatalytic asymmetric vinylogous Michael addition

Regioselective and diastereodivergent γ-position asymmetric vinylogous Michael addition (AVMA) of cyclohex-2-enones to nitroalkenes and γ′-AVMA between cyclohex-3-enones and nitroalkenes.

Exploration of 1,3-dipolar cycloaddition reactions to construct the core skeleton of Calyciphylline A-type alkaloids

Nitrone induced 1,3-dipolar [3 + 2] cycloadditions were studied to construct the core structure of Calyciphylline A-type Daphniphyllum alkaloids.

A bioinspired approach for construction of the [7-5-6-5] all-carbon tetracyclic core of logeracemin A

An efficient successive Michael/double aldol/dehydration reaction approach for the spiro-linked DEFF′ tetracyclic core ring systems of logeracemin A was developed.

Synthetic studies on daphniglaucins

The synthetic approach to the core framework of daphniglaucin-type Daphniphyllum alkaloids is described herein.

Construction of the [6,5,7,5] Tetracyclic Core of Calyciphylline A Type Alkaloids via a Tandem Semipinacol Rearrangement/Nicholas Reaction

A novel and efficient approach toward the assembly of the synthetically challenging tetracyclic [6,5,7,5] core structure of calyciphylline A-type alkaloids is developed. The synthetic route features a tandem semipinacol rearrangement/Nicholas reaction that has been devised strategically to construct the spirocyclic A/B ring and the sterically congested vicinal all-carbon quaternary carbon centers in high diastereoselectivity. Late-stage installation of the hydropyrrole ring and the strained 7-membered ring via a double-reductive amination and ring-closing metathesis, respectively, has also been realized.

Recent Progress in the Chemistry of Daphniphyllum Alkaloids †

Daphniphyllum is an evergreen species known since 1826. After initial systematic investigations, more than 320 members of this family have been isolated, which comprise complex and fascinating structures. Unique azapolycyclic architectures containing one or more quaternary stereocenters render these alkaloids synthetically challenging. This review covers efforts toward the synthesis of Daphniphyllum alkaloids spanning the period from 2005 to the beginning of 2016, including reported biological activities as well as the isolation of new members of this genus.

The daphniphyllum alkaloids: total synthesis of (-)-calyciphylline N

Presented here is a full account on the development of a strategy culminating in the first total synthesis of the architecturally complex daphniphyllum alkaloid, (-)-calyciphylline N. Highlights of the approach include a highly diastereoselective, intramolecular Diels-Alder reaction of a silicon-tethered acrylate; an efficient Stille carbonylation of a sterically encumbered vinyl triflate; a one-pot Nazarov cyclization/proto-desilylation sequence; and the chemoselective hydrogenation of a fully substituted diene ester.

Direct construction of vicinal all-carbon quaternary stereocenters in natural product synthesis

Molecules containing vicinal all-carbon quaternary stereocenters are found in many secondary metabolites, and they exhibit a variety of biological and pharmacological activities.

Strategies towards the synthesis of calyciphylline A-type Daphniphyllum alkaloids

The Daphniphyllum alkaloids are a diverse family of natural products rich in number and structural diversity that have been known for many decades. However, the structurally unique subclass of calyciphylline A-type alkaloids has only recently been discovered and is relatively unexplored. Several noteworthy core syntheses and the development of a wide range of novel synthetic strategies have been achieved. This includes strategies based on intramolecular Michael addition, Pd-catalysis, cycloaddition, and Mannich-type reactions. This review will provide an overview of these synthetic studies.

Rapid access to the heterocyclic core of the calyciphylline A and daphnicyclidin A-type Daphniphyllum alkaloids via tandem cyclization of a neutral aminyl radical

A streamlined approach to the tertiary amine-containing core of the calyciphylline A and daphnicyclidin A-type Daphniphyllum alkaloids is presented. A known carvone derivative is converted into the core structure in only four synthetic operations, and it is well poised for further elaboration. The key enabling methodology is a radical cyclization cascade beginning with addition of a secondary, neutral aminyl radical to the β-position of an enone, followed by trapping with a pendant alkyne.

Propargylic cation-induced intermolecular electrophilic addition–semipinacol rearrangement

A novel propargylic electrophile-induced tandem intermolecular addition–semipinacol rearrangement was developed for the synthesis of a series of synthetically useful β-propargyl spirocyclic ketones. Its synthetic application was demonstrated by efficient construction of the key tricyclic moiety of daphlongamine E.