Synthesis of the azocino[4,3-b]indole core structure for the synthesis of strychnos alkaloids

Diastereoselective synthesis of 3,4-dihydro-2H-pyran-4-carboxamides through an unusual regiospecific quasi-hydrolysis of a cyano group

An efficient diastereoselective approach for the synthesis of functionalized 3,4-dihydro-2H-pyran-4-carboxamides with variable frame was developed based on the reaction of available 4-oxoalkane-1,1,2,2-tetracarbonitriles (adducts of TCNE and ketones) with aldehydes in an acidic media. An unusual process of quasi hydrolysis of the cyano group was observed in the course of the described regio- and diastereoselective transformation.

Concise total synthesis of (±)-aspidospermidine

(±)-Aspidospermidine (1) has been synthesized from the commercially available 2,3-dihydro-1H-carbazol-4(9H)-one 6 in 10 steps with 20% overall yield. The key step of the strategy is a one-pot carbonyl reduction/iminium formation/intramolecular conjugate addition reaction that may be applied for the synthesis of other Aspidosperma alkaloids.

Domino-synthesis and fluorescence properties of 4-cyano-2-oxo-1,2-dihydropyridine-3-carboxamides and 2-oxo-1,2-dihydropyridine-3,4-dicarbonitriles

Non-catalytic conversion of 4-oxoalkane-1,1,2,2-tetracarbonitriles in the presence of water leads to the mixture of fluorescent 4-cyano-2-oxo-1,2-dihydropyridine-3-carboxamides and 2-oxo-1,2-dihydropyridine-3,4-dicarbonitriles in equal proportions.

3,9-Dimethyl-2,3-dihydro-spiro-[carb-az-ole-1,2'-[1,3]dithio-lan]-4(9H)-one

The title compound, C₁₆H₁₇NOS₂, consists of a carbazole skeleton with methyl and dithiol­ane groups as substituents. In the indole ring system, the benzene and pyrrole rings are nearly coplanar, forming a dihedral angle of 1.02 (11)°. The cyclo­hexenone ring has a twisted conformation, while the dithiol­ane ring adopts an envelope conformation with one of the CH₂ C atoms at the flap. In the crystal, weak C—H⋯O hydrogen bonds link the mol­ecules into supra­molecular chains nearly parallel to the c axis. These hydrogen bonds together with weak C—H⋯π inter­actions link the molecules into a three-dimensional supramolecular network.

Total synthesis of (+)-condylocarpine, (+)-isocondylocarpine, and (+)-tubotaiwine

The first enantioselective total syntheses of indole alkaloids of the condylocarpine type are reported. (+)-Condylocarpine, (+)-isocondylocarpine, and (+)-tubotaiwine were prepared in high enantiomeric purity (er > 99:1) from (1S,5R)-hexahydro-1,5-methano-1H-azocino[4,3-b]indole-12-one 7b by way of five or six isolated intermediates.

Total synthesis of (+/-)- and (-)-actinophyllic acid

Development of efficient sequences for the total syntheses of (+/-)-actinophyllic acid (rac-1) and (-)-actinophyllic acid (1) are described. The central step in these syntheses is the aza-Cope/Mannich reaction, which constructs the previously unknown hexacyclic ring system of actinophyllic acid in one step from much simpler tetracyclic precursors. The tetracyclic hexahydro-1,5-methano-1H-azocino[4,3-b]indole ketone rac-37 is assembled from o-nitrophenylacetic acid in four steps, with oxidative cyclization of a dienolate derivative of tricyclic precursor rac-35 being the central step. In the first-generation synthesis, this intermediate is transformed in two steps to homoallyl amine rac-43, whose formaldiminium derivative undergoes efficient aza-Cope/Mannich reaction to give pentacyclic ketone rac-44. In four additional steps, this intermediate is advanced to (+/-)-actinophyllic acid. The synthesis is streamlined by elaborating ketone rac-37 to beta-hydroxyester intermediate rac-53, which is directly transformed to (+/-)-actinophyllic acid upon exposure to HCl and paraformaldehyde. This concise second-generation total synthesis of (+/-)-actinophyllic acid is realized in 22% overall yield from commercially available di-tert-butyl malonate and o-nitrophenylacetic acid by a sequence that proceeds by way of only six isolated intermediates. The first enantioselective total synthesis of (-)-actinophyllic acid (1) is accomplished by this direct sequence from tricyclic keto malonate (S)-35. Catalytic enantioselective reduction of alpha,beta-unsaturated ketone 66 is the key step in the preparation of intermediate (S)-35 from the commercially available Boc-amino acid 65. Discussed also is the possibility that the aza-Cope/Mannich reaction might be involved in the biosynthesis of (-)-actinophyllic acid.

Scope and mechanism of intramolecular aziridination of cyclopent-3-enyl-methylamines to 1-azatricyclo[2.2.1.0(2,6)]heptanes with lead tetraacetate

A series of seven cyclopent-3-en-1-ylmethylamines bearing one, two, or three methyl substituents at the C2, C3, C4, or C(alpha) positions, including the unsubstituted parent, was accessed by ring-closing metatheses of alpha,alpha-diallylacetonitrile (or methallyl variants) and alpha,alpha-diallylacetone followed by hydride reductions or reductive amination, or by Curtius degradations of alpha,alpha-dimethyl- and 2,2,3-trimethylcyclopent-3-enylacetic acids. Oxidation of the primary amines with Pb(OAc)(4) in CH(2)Cl(2), CHCl(3) or benzene in the presence of K(2)CO(3) effected efficient intramolecular aziridinations, in all cases except the alpha-methyl analogue (16), to form the corresponding 1-azatricyclo[2.2.1.0(2,6)]heptanes, including the novel monoterpene analogues, 1-azatricyclene and the 2-azatricyclene enantiomers. The cumulative rate increases of aziridination reactions observed by (1)H NMR spectroscopy in CDCl(3) resulting from the presence of one or two methyl groups on the cyclopentene double bond, in comparison to the rate of the unsubstituted parent amine (1:17.5:>280), indicate a highly electrophilic intermediate as the nitrene donor and a symmetrical aziridine-like transition state. A mechanism is outlined in which the amine displaces an acetate ligand from Pb(OAc)(4) to form a lead(IV) amide intermediate RNHPb(OAc)(3) proposed as the actual aziridinating species.