RESUMO
Unsaturated and doubly unsaturated esters have been synthesized in two steps by the application of a radical xanthate transfer process of a simple methylsulfoxide starting material to a range of terminal alkenes. syn-Elimination of the sulfoxide gives α,ß-unsaturated esters, which coupled with a xanthate elimination yields α,ß,γ,δ-unsaturated esters.
RESUMO
Two syntheses of the Amaryllidaceae alkaloid clivonine (1) are described. Both employ previously reported 7-arylhydrindane 6 as an intermediate but differ in the method employed for subsequent introduction of what becomes the ring-B lactone carbonyl carbon (C7). The synthesis featuring a Bischler-Napieralski reaction for this transformation constitutes the first asymmetric synthesis of natural (+)-clivonine. Crystal structures for compounds (±)-13, (±)-16, (-)-20 and (±)-28 are also reported.
Assuntos
Alcaloides de Amaryllidaceae/síntese química , Magnoliopsida/química , Modelos Moleculares , Estrutura MolecularRESUMO
An efficient synthesis of (±)-trans,cis-4-hydroxy-5,6-di-O-isopropylidenecyclohex-2-ene-1-one (3) has been developed from acetonide-protected meso-1,2-dihydrocatechol derivative 1 via photooxygenation, then Kornblum-DeLaMare rearrangement. The product is unstable unless its 4-hydroxy group is protected, as it undergoes facile dimerization in solution to a 1:1 mixture of diastereoisomeric decahydrodibenzofurans 8 and 9. A new synthesis of the dihydrocatechol 1 from 1,3-cyclohexadiene has also been developed.
Assuntos
Benzofuranos/química , Cicloexenos/química , Cicloexenos/síntese química , Estrutura Molecular , EstereoisomerismoRESUMO
A fully diastereoselective total synthesis of the lycorenine-type Amaryllidaceae alkaloid (+/-)-clivonine (19) is reported via a route that employs for the first time a biomimetic ring-switch from a lycorine-type progenitor, thereby corroborating experimentally the biogenetic hypothesis first expounded for these compounds by Barton in 1960.
