Isolation and synthesis of biologically active carbazole alkaloids

Generating diverse structures with a minimum amount of synthetic effort is an important goal for drug discovery. Here, the authors report a two-phase synthesis for the generation of skeletally diverse small molecules—forming molecular scaffolds and subsequently diversifying each into multiple structures.

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De novo branching cascades for structural and functional diversity in small molecules

The synthesis of carbocyclic eight-membered rings

Progress in the construction of cyclooctanoid systems: new approaches and applications to natural product syntheses.

2.3.1. IMDA Reactions of Acetylenic Sulfones 4512 2.3.2. IMDA Reactions of Allenic Sulfones 4513 2.3.3. IMDA Reactions of Dienyl Sulfones 4513 3. 1,3-Dipolar Cycloadditions 4514 3.1. With Azides 4514 3.2. With Diazo Compounds 4515 3.3. With Nitrones 4516 3.4. With Nitrile Oxides 4519 3.5. With Mesoionic Compounds 4519 3.6. With Other 1,3-Dipoles 4519 4. [2 + 2] Cycloadditions 4520 4.1. With Alkenes and Dienes 4520 4.2. Intramolecular [2 + 2] Cycloadditions 4522 4.3. With Imines, Enamines, Ynamines, And Enol Ethers 4522 4.4. Other [2 + 2] Cycloadditions 4523 5. Miscellaneous Cycloadditions 4524 6. Ene Reactions 4524 7. Cyclizations of Bis(allenic) Sulfones and Their Congeners 4526

Cycloadditions and cyclizations of acetylenic, allenic, and conjugated dienyl sulfones.

Hetero-cope rearrangements - vI1 short and stereoselective syntheses of 2-vinylindoles by a tandem-process

Stereoselective Synthesis of Taxane Derivatives



Substituted racemic 4,8,12-trinortaxanes were prepared stereoselectively in several steps from the dienone 10. A variant of the de Mayo reaction with bicyclononenones 4 and cyclohexen produced the desired configuration at C(8) of the taxane framework. Retro-aldol cleavage of the tetracycle 5 led to the taxane skeleton 6. Stereoselective reduction followed by treatment with base afforded 7b. Hydrolysis of the acetal group and further reduction yielded 9 in which the relative configuration corresponds to the one of the natural products.

Stereoselektive Synthesen von Taxan‐Derivaten

Unsaturated Hydrindanone Derivatives from Arenes by Hetero‐Claisen Rearrangement

Publisher Summary This chapter discusses (1) hemisyntheses based on the taxol molecule and on deacetylbaccatin III, (2) total synthesis of the taxane skeleton as well as certain polyfunctional derivatives, and (3) development of the pharmacology of taxol and its derivatives. The six-membered A ring, a distorted boat, is cis-fused to the eight-membered B ring which, in turn, has a boat-chair conformation. Carbon-13 NMR is applied to the specific study of taxanes having an epoxide or oxetane functionality. Taxanes having a 4–20 epoxide originates from derivatives with an exocyclic double bond at these positions, whereas the oxetane ring may be the result of opening of the epoxide followed by rearrangement. The biological activity of taxanes especially that of taxol, together with the synthetic challenge of the strained and highly functionalized tricycles led to constantly increasing interest, resulting in much preparative work. Biomimetic cyclization reaction is used successfully to synthesize terpenoids.

Siegfried Blechert

Papers

Hetero-cope rearrangements - vI1 short and stereoselective syntheses of 2-vinylindoles by a tandem-process

Stereoselektive Synthesen von Taxan‐Derivaten

Unsaturated Hydrindanone Derivatives from Arenes by Hetero‐Claisen Rearrangement

Chapter 6 Taxus Alkaloids

Ungesättigte Hydrindanonderivate aus Arenen durch Hetero-Claisen-Umlagerung†