RESUMO
Treatment of germacrone (1) with different electrophiles, and of its epoxy derivatives germacrone-4,5-epoxide (2), germacrone-1,10-epoxide (3) and isogermacrone-4,5-epoxide (4) with Brönsted/Lewis acids and Ti(III), gives rise to a great structural diversity. Thus, by using a maximum of two steps, the production of more than 40 compounds corresponding to 14 skeletons is described. Computational calculations rationalizing the structural divergence produced are also described. Finally, since some of the compounds generated are bioactive natural sesquiterpenes, the mechanisms of formation of these substances will provide new insights in their biosynthesis.
Assuntos
Compostos de Epóxi/química , Modelos Teóricos , Sesquiterpenos de Germacrano/química , Ciclização , Ácidos de Lewis/química , Estrutura Molecular , Sesquiterpenos de Germacrano/síntese químicaRESUMO
As a result of a combined theoretical and experimental study, we describe a two-step protocol for the preparation of an optically pure, multifunctional, cyclopentanic core shared by a number of natural products. This process is based on a hitherto unreported Ti(III)-mediated diastereoselective cyclization in which the hydroxy-directed template effect played by the Ti(III) species was found to be crucial for the stereoselective outcome of the reaction. The viability of this concept was confirmed with the first protecting-group free synthesis of three enantiopure chokols, namely, chokols K, E, and B.
RESUMO
Highly efficient preparations of anticancer ß-elemene and other bioactive elemanes were carried out using the natural product germacrone as a renewable starting material. The syntheses were achieved in only 3-5 steps with excellent overall yields (43-54%). An enantioselective approach to these molecules is also described.
Assuntos
Antineoplásicos/síntese química , Sesquiterpenos de Germacrano/química , Sesquiterpenos/síntese química , Catálise , Estrutura Molecular , Paládio/química , EstereoisomerismoRESUMO
The transannular cyclization of germacrone with HSO(3)Cl at -78 degrees C by means of a concerted and regioselective mechanism gives rise to a bicyclo[6.2.0]decan-2-ylium intermediate ion, which evolves to unusual skeletons through subsequent cyclization and Wagner-Meerwein rearrangements. This novel germacra-1(10),4-diene cyclization could suggest the existence of a new biosynthetic pathway to sesquiterpenes.
Assuntos
Sesquiterpenos de Germacrano/síntese química , Ciclização , Estrutura Molecular , Sesquiterpenos de Germacrano/química , EstereoisomerismoRESUMO
Regioselective halogenation of the terminal isopropylidene unit of different acyclic polyolefinic polyprenoids (farnesyl acetate, geranylgeranyl acetate, squalene, etc.) using NCS/catalytic polymer-supported selenenyl bromide is described; good to excellent yields are obtained (68-96%). The first applications of this protocol include the concise synthesis of bioactive terpenoids 1-3.