RESUMO
A tricyclic core containing a 5,7-fused bicyclic unit of rameswaralide was prepared starting from a 1,6-enyne. The synthetic sequence involved (i) ruthenium-catalyzed [5+2]-cycloaddition of 1,6-enyne, (ii) an acyl radical based approach to construct the lactone, and (iii) a regioselective installation of the conjugated double bond by a concomitant sulfenylation-dehydrosulfenylation sequence.
RESUMO
The Ru-catalyzed intramolecular [5+2] cycloaddition of cyclopropylenynes is investigated with respect to the regio- and diastereoselectivity as well as the functional group compatibility of the reaction. Evidence for the mechanism as occurring through a ruthenacyclopentene intermediate is elucidated from 1) the study of the diastereoselectivity of the cycloaddition; 2) the effect of variation of substituents on the regioselectivity of cyclopropyl bond cleavage in 1,2-trans- and 1,2-cis-disubstituted cyclopropanes and 3) examples that clearly do not involve ruthenacyclohexene as intermediates as products still incorporate the cyclopropyl moiety. The scope and limitations of the Ru-catalyzed cycloaddition are discussed and compared with the Rh-catalyzed reaction. The potential power of this methodology towards natural product total synthesis is demonstrated by the formation of several polycyclic systems with the chosen reaction conditions and readily available cyclopropylenyne substrates.
Assuntos
Rutênio/química , Alcenos/química , Produtos Biológicos/química , Catálise , Cristalografia por Raios X , Ciclização , Isomerismo , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Estrutura MolecularRESUMO
[reaction: see text]. Ru-catalyzed cycloisomerization of cyclopropylenynes proceeds with good to high diastereoselectivities to form hexahydroazulenes.
Assuntos
Ciclização , Rutênio/química , Alcenos/química , Alcinos/química , Azulenos , Catálise , Cristalografia por Raios X , Cicloeptanos/química , Ciclopropanos/química , Conformação Molecular , Estrutura Molecular , EstereoisomerismoRESUMO
The first copper(I) bromide/Quinap-catalyzed synthesis of enantiomerically enriched propargylamines by addition of alkynes to enamines is reported. Various functionalized terminal alkynes add smoothly to Nprotected enamines to afford the corresponding amines in good to high yields and moderate to good enantiomeric excesses. The influence of the metal salt, the ligand, and the protecting group on the conversion, the reaction rate, and the stereoselectivity of the reaction are investigated. The scope of the reaction and further transformations of the resulting propargylamines (deprotection, Pauson-Khand reaction) are also described.
