Synthetic approaches toward naphthyridinomycin. I. Stereoselective synthesis of a tetracyclic intermediate.

A highly stereoselective synthesis of a tetracyclic intermediate $\text{4}$ to the quinone antitumor antibiotic naphthyridinomycin $\text{1}$ is described.     

Synthetic studies toward the mitomycins: construction of the tetracyclic core via a reductive aminocyclization reaction

The tetracyclic core of the mitomycin family of natural products has been formed in one step from an acyclic precursor via a reductive aminocyclization reaction. Additionally, the eight-membered benzazocine can be prepared without the need for prior activation of the aniline. Construction of a mitomycin K analogue lacking the C9a methoxy moiety is also reported herein.     

Synthetic studies on (+)-aplasmomycin. 2. Stereoselective synthesis of Corey''s key intermediate, a formal total synthesis

The C-3 C-11 segment of (+)-aplasmomycin was synthesized stereoselectively starting from (+)-pantolactone ( ) and the C-3 C-17 segment was synthesized via coupling of and .     

Synthetic approaches toward sesterterpenoids

Sesterterpenoids account for many bioactive natural products, often with unusual and complex structural features, which makes them attractive targets for synthetic chemists. This review surveys efforts undertaken toward the synthesis of sesterterpenoids, focusing on completed total syntheses and covering ca. 50 natural products in total.     

Synthetic approaches toward the reserpine

Reserpine is an indole alkaloid, antipsychotic, and antihypertensive drug that has been used for the control of high blood pressure and for the relief of psychotic symptoms. It was first isolated in 1952 from the dried root of Rauwolfia serpentina whose molecular structure was established in 1953 and natural configuration was published in 1955. The first total synthesis of reserpine was reported by Woodward in 1958. This review article updates current multistep synthetic approaches toward the reserpine natural product and its analogues.     

Stereoselective synthesis of tetracyclic indolines via gold-catalyzed cascade cyclization reactions

A reliable synthetic route to fused polycyclic indolines is documented by the development of a stereoselective gold catalyzed cascade cyclization of indole propargylic alcohols.     

Preparation of a functionalized tetracyclic intermediate for the synthesis of rhodexin A

An efficient synthesis of the tetracyclic steroid core, 19, of rhodexin A and sarmentogenin is reported. An initial inverse-electron-demand Diels-Alder reaction of the acyldiene 6 with the silyl enol ether 7a gave the cycloadduct 8 with the required four contiguous stereocenters in a single step. This compound was then transformed into the methylated enedione 13 which afforded after a reductive alkylation and annulation sequence the tetracycle 19.     

Synthetic studies toward the kempane diterpenes. Construction of a key tricyclic intermediate

A synthetic sequence is described for construction of the tricyclic portion (35) of kempane diterpenes. The central stereochemistry was established by a Diels-Alder addition of 2,6-dimethyl-para-benzoquinone to a 5-membered, dithiane-protected diene, and the addition of acetylide, with very high chemoselectivity, provided a suitably functionalized handle that will be incorporated into the final seven-membered ring. The remaining stereogenic centres about the decalin moiety were established by a series of equilibration and reduction steps.     

Synthetic approaches toward macrocyclic sulfonyl crown formazans

Coupling of diazonium salts with ethyl sulfonylpyruvates 1–3 or arenesulfonylacetic acids 14,15 afforded good yields of the corresponding 1,5-symmetrically disubstituted-3-sulfonylformazans 4–11. The new sulfonyl macrocyclic crown formazans 25–32 were prepared by coupling of the appropriate bisdiazonium salts 22–24 with compounds 1–3 or 14,15. © 1996 John Wiley & Sons, Inc.     

Synthetic studies toward 13-oxyingenol: construction of the fully substituted tetracyclic compound

13-Oxyingenol and its derivatives have high levels of anti-HIV activity. A fully substituted tetracyclic skeleton of 13-oxyingenol is constructed by using spiro-cyclization and ring-closing olefin metathesis as key steps.     

Meldrum's acid-derived thione dienophile in a convergent and stereoselective synthesis of a tetracyclic quassinoid intermediate

An advanced intermediate toward anti-cancer quassinoids has been synthesized using a quadruple diene-transmissive [4+2]-cycloaddition strategy. High convergence is achieved thanks to a regio- and stereoselective hetero-Diels-Alder reaction using a thione. The relative stereochemistry of the final Diels-Alder adduct was controlled by tethered substituents introduced via a highly syn- and gamma-selective vinylogous Mukaiyama aldol.     

Synthetic study of tetramethyljulolidine—a key intermediate toward the synthesis of the red dopant DCJTB for OLED applications

The formation and characterization of a novel chiral sulfonic acid derivative obtained during the synthesis of 1,1,7,7-tetramethyljulolidine (TMJ), a key intermediate towards the red dopant 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) used for organic electroluminescent devices, upon bis-annulation of N,N-bis(4-methyl-2-butenyl)aniline is described.     

Synthetic studies on maitotoxin. 3. Stereoselective synthesis of the BCDE-ring system

The stereoselective synthesis of the BCDE-ring system of maitotoxin has been accomplished through a two-directional strategy for the construction of polycyclic ether. The key reactions involve SmI 2-induced double cyclization of a beta-alkoxyacrylate and a double dihydroxylation for construction of the B- and E-rings.     

Synthetic studies on maitotoxin. 2. Stereoselective synthesis of the WXYZA'-ring system

The stereoselective synthesis of the WXYZA'-ring system of maitotoxin has been accomplished via a linear synthetic approach, in which key reactions were SmI 2-induced cyclization of beta-alkoxyacrylate for the construction of the A'-, Y-, and X-rings and 6- endo cyclization of hydroxy vinylepoxide for that of the Z- and W-rings.     

Synthetic approaches to cularines. I. Phenolic oxidative coupling

Ferricyanide-promoted biogenetic-type phenolic oxidative coupling of an 8,3′-dihydroxytetrahydrobenzyl-isoquinoline 19a afforded the isomeric phenolic cularines 5 and 21. Vanadium oxytrifluoride oxidation of the N-borane complex of 19a afforded, regioselectively, the para-coupled product 21. Moreover, when this reagent was used on the monophenolic tetrahydrobenzylisoquinoline 19b protected as its N-borane complex, cularine 1 was regioselectively obtained in good yield. Other structural modifications and reagents were not successful.     

Synthetic studies on mitomycins. 2. A synthesis of 9a-hydroxy-5,8-dideoxomitosane skeleton through a novel retroaldol type of ring-opening reaction.

A synthesis of 9a-hydroxy-5,8-dideoxomitosanes was accomplished by the transannular cyclization of hydro-1-benzazocinone intermediates derived from 3-(2,5-dioxo-1-methylcyclopentyl)-6-methyl-p-phenylenediamine derivatives. These mitosanes were led to the 8-membered ring system by an oxidative ring-opening reaction.     

Synthetic efforts toward the synthesis of octalactins

Octalactin B was synthesized from the commercially available methyl-3-butenoate and isobutyraldehyde, using enantioselective allyl- and crotyltitanations to control the stereogenic centers at C3, C4, C7, C8, and C13. Moreover, the two other key-step reactions are a cross-metathesis reaction and a lactonization, using the effective anhydride MNBA, to build up the eight-membered ring lactone.