Total Synthesis of (−)-Sacidumlignans B and D

A Concise Synthesis of Sacidumlignan B

A short synthesis of racemic Sacidumlignan B was achieved for the first time. The key steps included a formal reductive coupling between the diaryl ketone and the crotyl bromide, and the subsequent Friedel–Crafts cyclization, which led to an efficient construction of dihydronaphthalene skeleton in this 2,7′-cyclolignan natural product.

Recent strategies and tactics for the enantioselective total syntheses of cyclolignan natural products

Covering: 2000 to 2021Lignan natural products are found in many different plant species and possess numerous useful biological properties, such as anti-inflammatory, antiviral, antioxidant, antibacterial, and antitumor activities. Their utility in both traditional and conventional medicine, coupled with their structural diversity has made them popular synthetic targets over many decades. This review specifically addresses the cyclolignan subclass of the family, which possess both a C8-C8' and a C2-C7' linkage between two different phenylpropene units. We present a comprehensive overview of the diverse strategies employed by chemists to achieve enantioselective total syntheses of cyclolignans covering: 2000 to 2021.

Recent advances in the total synthesis of 2,7'-cyclolignans

The synthetic progress of bioactive 2,7'-cyclolignans is reviewed. After a short introduction to biosynthesis and chemoenzymatic synthesis, the chemical synthesis of various aryltetralin, dihydronaphthalene and 7'-arylnaphthalene-types of these lignans is demonstrated. Notably, newly developed methods, such as Pd-catalyzed C-H arylation, organocatalysis and photocatalysis under visible-light, are discussed during the construction of their skeleton. These efforts will stimulate further development of novel synthetic strategies for this kind of natural product with important biological activities.

Syntheses of Gymnothespirolignans B and C and Non-natural Isomer 9-Epi-gymnothespirolignan B

Syntheses of polycyclic spiro lignans gymnothespirolignans B and C as well as the unnatural isomer 9-epi-gymnothespirolignan B were accomplished using (R)-Roche ester and an appropriately substituted fluorenone. Key features of the convergent syntheses include coupling of the fluorenone and an iodo-alkene intermediate derived from (R)-Roche ester in the presence of the Lewis acid TiCl(OiPr)₃, C9-O bond formation via an S_N2 reaction with retention of stereochemistry, and diastereoselective hydrogenations of a common alkene intermediate guided by accessibility or positioning by the C8-methoxy.

C-Alkylation of alkali metal carbanions with olefins

C-Alkylations of alkali metal carbanions with olefins, first reported five decades ago, is a class of reaction undergoing a resurgence in organic synthesis in recent years. As opposed to expectations from classical chemistry and transition metal-catalysis, here olefins behave as closed-shell electrophiles. Reactions range from highly reactive alkyllithiums giving rise to anionic polymerization, to moderately reactive alkylpotassium or alkylsodium compounds that give rise to defined, controlled and bimolecular chemistry. This review presents a brief historical overview on C-alkylation of alkali metal carbanions with olefins (typically mediated by KOtBu and KHMDS), highlights contemporary applications and features developing mechanistic understanding, thereby serving as a platform for future studies and the widespread use of this class of reaction in organic synthesis.

Synthesis of the Tetracyclic Framework of Polycyclic Spiro Lignan Natural Products

Polycyclic spiro lignans are a new family of lignan natural products recently isolated from Gymnotheca involucrata. The first synthesis of two model substrates of this rare family of natural products was achieved in six steps. An efficient strategy that features Suzuki coupling and Friedel-Crafts acylation was employed to construct the ABC tricyclic fluorene framework. Subsequently, Grignard reaction followed by acid-mediated cyclization furnished the spiro cyclic ether ring D.

Base-promoted addition of DMA with 1,1-diarylethylenes: application to a total synthesis of (-)-sacidumlignan B

A base-promoted addition of DMA (N,N-dimethylacetamide) to 1,1-diarylethylenes has been developed, and it provides a new strategy for the synthesis of N,N-dimethyl-4,4-diarylbutanamides from 1,1-diarylethylenes at room temperature. This method allows us to achieve the goal of synthesizing (-)-sacidumlignan B, and provides simple operation and broad substrate scope by avoiding the use of transition metal catalysts.

Concise Synthesis of (+)-β- and γ-Apopicropodophyllins, and Dehydrodesoxypodophyllotoxin

Herein, we present an expeditous synthesis of bioactive aryldihydronaphthalene lignans (+)-β- and γ-apopicropodophyllins, and arylnaphthalene lignan dehydrodesoxypodophyllotoxin. The key reaction is regiocontrolled oxidations of stereodivergent aryltetralin lactones, which were easily accessed from a nickel-catalyzed reductive cascade approach developed in our group.

Total synthesis of sinenside A

The first total synthesis of norlignan glucoside sinenside A has been accomplished. An intramolecular acetalization reaction has been employed as the key skeletal construct to forge the central cyclic disaccharide core. The trans-1,2-diol configuration present in the cyclic disaccharide of this natural product is unique and has been addressed by setting this configuration at the beginning. A 1,2-orthoester group has been selected as a handle for both sp glycosidation and for differentiation of the C2'-OH (that participates in the key acetalization reaction) of the sugar unit.

Stereocontrolled syntheses of tetralone- and naphthyl-type lignans by a one-pot oxidative [3,3] rearrangement/Friedel-Crafts arylation

The development of a stereoselective one-pot oxidative [3,3] sigmatropic rearrangement/Friedel-Crafts arylation that provides enantioenriched benzhydryl compounds is reported. The utility of this new transformation is demonstrated by the concise synthesis of several tetralone- and naphthyl-type lignan natural products, many of which display anti-malarial activity.