The first total synthesis of the alkaloid (−)-haliclonin A is reported. The asymmetric synthesis relied on a novel organocatalytic asymmetric conjugate addition of nitromethane with 3-alkenyl cyclohex-2-enone to set the stereochemistry of the all-carbon quaternary stereogenic center. The synthesis also features a Pd-promoted cyclization to form the 3-azabicyclo[3,3,1]nonane core, a SmI₂-mediated intermolecular reductive coupling of enone with aldehyde to form the requisite secondary chiral alcohol, ring-closing alkene and alkyne metathesis reactions to build the two aza-macrocyclic ring systems, and an unprecedented direct transformation of enol into enone.

The first total synthesis of the alkaloid (−)-haliclonin A is reported. The asymmetric synthesis relied on a novel organocatalytic asymmetric conjugate addition of nitromethane with 3-alkenyl cyclohex-2-enone to set the stereochemistry of the all-carbon quaternary stereogenic center. The synthesis also features a Pd-promoted cyclization to form the 3-azabicyclo[3,3,1]nonane core, a SmI₂-mediated intermolecular reductive coupling of enone with aldehyde to form the requisite secondary chiral alcohol, ring-closing alkene and alkyne metathesis reactions to build the two aza-macrocyclic ring systems, and an unprecedented direct transformation of enol into enone.

A versatile and divergent two-step transformation of malimides to racemic tetramates and tetramic acids is described. The method consists of Grignard reagent addition with malimides to give hemiaminals and concentrated HCl-promoted chemoselective transformations of the latter. When running the reaction in CH₂Cl₂ and in the presence of 2.5 molar equiv. of conc. HCl, 5-alkyltetramates were formed, while in neat conc. HCl, 5-alkyltetramic acids were obtained. Using this method, a variety of title compounds were prepared in good to excellent yields (82%–99%, and 76%/85%). The work also constitutes a formal racemic total synthesis of reutericyclin. On the basis of the experimental evidences and of a deuterium labeling experiment, a plausible reaction mechanism was proposed. This work thus demonstrated two new types of step economical and chemodivergent transformations starting from malic acid.

We report the concise and protecting-group-free enantioselective total syntheses of circumdatins F and H. In view of the extreme importance of analogs of quinazolinone alkaloids in drug research and discovery, four analogs of bioactive quinazolinobenzodiazepine alkaloids, including demethoxycircumdatin H (12) and N-demethylbenzomalvin A (13), have been synthesized. The method is based on the low-valent titanium-promoted intramolecular reductive coupling of imides with o-nitrobenzimides, which yielded quinazolino[3,2-a][1,4]benzodiazepines under mild conditions. In addition, heptacyclic dehydraasperlicin E (16) has been synthesized from asperlicin C by a NCS-mediated dehydra-cyclization reaction.

Full details of the enantioselective four-step and five-step total syntheses of (−)-chaetominine from D-Trp and L-Trp are described. Featuring an oxidative double cyclization reaction, and tandem C14 epimerization-lactamization reactions as key steps, the method provides a rapid access to (−)-chaetominine (6a) and analogues. The total syntheses of (−)-chaetominine (6a) are so far the most concise and efficient. Through comprehensive investigation, the stereochemical requirements for the double cyclization reaction were revealed, and the confusion regarding physicochemical properties of this natural product was clarified. Moreover, short pathways to complexity generation, a scenarios revealed for the biosynthesis of fungal peptidyl alkaloid multi-cyclic scaffolds, have been validated through the chemical synthesis. On the basis of these findings, a plausible biosynthetic pathway for (−)-chaetominine (6a) was suggested.

The vinylogous Mannich reaction (VMR) between 2-(tert-butyldimethylsilyloxy)furan (TBSOF) and (R_S)-t-BS-imine 12a and the application of the VMR adduct butenolide 13a as a versatile chiral building block for the synthesis of hydroxylated piperidine alkaloids and azasugars were investigated. Firstly, both the anti diastereoselectivity and the chemical yield of the asymmetric VMR between TBSOF and (R_S)-t-BS-imine 12a were improved by the use of Sm(OTf)₃/H₂O (1.5 equiv.) as the promoter. Similar diastereoselectivities were also obtained with Yb(OTf)₃/H₂O, Cu(OTf)₂/H₂O, Zn(OTf)₂/H₂O, or the Brønsted acids TfOH or MsOH as the promotors. Secondly, an efficient four-step procedure for the elaboration of butenolide 13a into piperidine alkaloid (–)-deoxoprosophylline (2) was established. Thirdly, by taking advantage of the olefin functionality in the butenolide 13a, polyhydroxylated δ-lactams 23 and 21, which are ready precursors of azasugars L-deoxyallonojirimycin (ent-7) and L-3-epi-fagomine (ent-6), were obtained in two and three steps, respectively, via dihydroxylated lactone 17. The easily available synthetic intermediate 17 can also serve as a key intermediate for the synthesis of the glycosyl nucleoside amino acid cores of polyoxins and nikkomycins.

Some Stemona alkaloids belonging to the tuberostemospironine group possess a spirolactone moiety with anti-configuration (C-9/C-9a). In this paper, we describe two approaches to this structural unity. By using bromine atom as a traceless directing group, the SmI₂-mediated reductive coupling of ketone 6 and β-bromomethacrylate proceeded with complete anti-diastereoselectivity. In the absence of an α-directing (chelation) group, the one-pot reaction of the ketone derived from alcohol 15 with the organozinc reagent generated from bromomethacrylate afforded spiro-α-methylene-γ-lactone derivative 16 as a single diastereomer. These two highly diastereoselective methods would find application in the synthesis of stemona alkaloids containing anti-configured spiro-lactone/pyrrolidine moieties. In addition, on the basis of our previous work, the total synthesis of (−)-9-epi-11-demethylsessilifoliamide J (11), and an improved synthesis of (−)-9,11-di-epi-sessilifoliamide J (9) were accomplished.

Amides are a class of highly stable and readily available compounds. The amide functional group constitutes a class of powerful directing/activating and protecting group for CC bond formation. Tertiary tert-alkylamine, including 1-azaspirocycle is a key structural feature found in many bioactive natural products and pharmaceuticals. The transformation of amides into tert-alkylamines generally requires several steps. In this paper, we report the full details of the first general method for the direct transformation of tertiary lactams/amides into tert-alkylamines. The method is based on in situ activation of amide with triflic anhydride/2,6-di-tert-butyl-4-methylpyridine (DTBMP), followed by successive addition of two organometallic reagents of the same or different kinds to form two CC bonds. Both alkyl and functionalized organometallic reagents and enolates can be used as the nucleophiles. The method displayed excellent 1,2- and good 1,3-asymmetric induction. Construction of 1-azaspirocycles from lactams required only two steps or even one-step by direct spiroannelation of lactams. The power of the method was demonstrated by a concise formal total synthesis of racemic cephalotaxine.

A chemo-, regio-, and stereoselectively controlled reaction is highly desirable, yet challenging in organic synthesis. Diversely substituted cis and trans isomers of 2-alkyl-3-pyrrolidinols, 5-alkyl-4-hydroxy-2-pyrrolidinones, β-hydroxy-γ-amino acids, and their higher homologues are key structural units found in numerous drugs, drug candidates, and bioactive natural products. Previously, we established a flexible approach to trans-5-alkyl-4-benzyloxy-2-pyrrolidinones 14 and trans-6-alkyl-5-benzyloxy-2-piperidinones 15. Herein, we report a direct, flexible, moisture insensitive, and highly diastereoselective approach to the corresponding cis diastereomers 16. This stereocontrolled method is based on the MsOH-mediated (Ms=methane sulfonyl) reductive dehydroxylation of hemiaminal 12 with NaBH(OAc)₃. cis-5-Alkyl-4-benzyloxy-2-pyrrolidinones 16 are useful building blocks for the syntheses of natural products such as (+)-preussin (4) and streptopyrrolidine (5) as well as (3S,4S)-γ-alkyl-β-hydroxy-γ-amino acids (6).

A novel strategy was developed for a rapid access to the naturally occurring racemic neoclausenamide and its analogs, which featured a highly erythro-selective vinylogous Mukaiyama type reaction (dr=12:1) and a highly diastereoselective tandem conjugate addition-Davis oxidation of N-Boc-pyrrol-2(5H)-one 5 (dr=10:1). Remarkably, the skeleton of neoclausenamide, namely 8a, an analog of neoclausenamide, was built in just two steps with all the four stereogenic centers (relative stereochemistry) established correctly and in excellent diastereoselectivities.

We describe efficient and flexible enantioselective syntheses of the active enantiomers of the pheromones of pine sawflies, including the species Diprion jingyuanensis, their homologs and, stereoisomers, as well as those identified from the Chinese species Diprion jingyuanensis, i.e., 126. A total of 48 compounds, including acetates 78–101 and propanoates 102–125, have been synthesized. Our general approach towards these compounds originated from the commercially available chirons diethyl (S)- and (R)-malates, as well as ethyl (R)-3-hydroxybutanoate. The Seebach asymmetric methylation was employed in a key step to control additional configuration.

The first enantioselective synthesis of cytotoxic natural products rigidiusculamides A (ent-21) and B (8) has been achieved by two synthetic routes. The first one is convergent based on the common intermediate 11, obtained through a high yielding SmI₂-mediated Reformatsky-type reaction. A highly diastereoselective one-pot Dess–Martin periodinane-mediated bis-oxidation allowed the direct conversion of the diastereomeric mixture of 11 into rigidiusculamide B (8). Isolation of minor diastereomer 21, in combination with computational work, allowed us to suggest the structure of the natural rigidiusculamide A to be 21, as synthesized by the second route. Four diastereomers (7, 7, 22a, and 22b) and an enantiomer (21) of rigidiusculamide A (21) have been synthesized. On the basis of literature precedents and computational work, a biosynthetic pathway for rigidiusculamides A and B was proposed to account for the opposite configuration at C-5 of those two congeners.

Five glutarimide alkaloids cordiarimide A (5), cordiarimide B (6), crotonimide A (3), crotonimide B (4), and julocrotine (2) have been synthesized starting from Boc-L-glutamine (7). The benzylic alcohol chiral centre of cordiarimides B (6) has been established in 6:1 diastereoselectivity by catalytic asymmetric hydrogenation using Zhou's catalytic system Pd(CF₃CO₂)₂/(R,R)-Me-DuPhos.

By using a methyl tetramate derivative (R)- or (S)-9 as a novel chiral building block, a direct, flexible, and highly enantioselective approach to methyl (R)- or (S)-5-alkyltetramates (2) is disclosed. Among the synthesized methyl 5-alkyltetramates 2, methyl 5-methyltetramate (2 a) is found in cytotoxic mirabimide E (4) and dysideapyrrolidone (5), and methyl 5-benzyltetramate (2 g) is a substructure in the potent antineoplastic dolastatin 15 (3). On the basis of this method, the first asymmetric synthesis of the antimitotic tetrapeptide belamide A (7) has been achieved in seven steps from (S)-9, with an overall yield of 23.8 %. Not only have the structure and absolute configuration of (+)-belamide A (7) been confirmed, but also the solvent used for recording the ¹³C NMR spectrum, the ¹³C NMR spectrum data correlation, and optical rotation data of natural belamide A (7) have been revised.

A concise enantioselective synthesis of the diazatricyclic core of alkaloid TAN1251C is reported. The method featured a stereoselective formation of the iodide intermediate 16b (in 2:1 ratio) from homoallylic amine 11b by iodine-promoted iodoaminocyclization, a previously claimed to be unsuccessful reaction. The intermediate 16b was converted to the tricyclic core of TAN1251C 28 in five steps. During this study, two unexpected products 22 and 25 were obtained, and compound 23, derived from 11a was shown to be unsuitable for the oxidative formation of the enamide of TAN1251C.

The asymmetric total synthesis of natural azasugars (+)-castanospermine, (+)-7-deoxy-6-epi-castanospermine, and synthetic (+)-1-epi-castanospermine has been accomplished in nine to ten steps from a common chiral building block (S)-8. The method features a powerful chiral relay strategy consisting of a highly diastereoselective vinylogous Mukaiyama-type reaction with either chiral or achiral aldehydes (≥95 % de; de=diastereomeric excess) and a diastereodivergent reduction of tetramic acids, which allows formation of three continuous stereogenic centers with high diastereoselectivities. The method also provides a flexible access to structural arrays of 5-(α-hydroxyalkyl)tetramic acids, such as 17/34, and 5-(α-hydroxyalkyl)-4-hydroxyl-2-pyrrolidinones, such as 18 and 25/35 a. The method constitutes the first realization of the challenging chiral synthons A and D and thus of the conceptually attractive retrosynthetic analysis shown in Scheme 1 in a highly enantioselective manner.