Ring contraction through epoxide rearrangement: A formal synthesis of capsorubin
An eight-step synthesis of the cyclopentane keto-alcohol 2, which has previously been converted in one step into the carotenoid pigment capsorubin (1), is described. The key step in our synthesis is a stereospecific epoxide rearrangement with ring contraction, thus producing the cyclopentane ring from an epoxide of a cyclohexene.
Constantino, Mauricio Gomes,Donate, Paulo Marcos,Frederico, Daniel,Carvalho, Tecia Vieira,Cardoso, Luiz Eduardo,Zukerman-Schpector, Julio
p. 3327 - 3340
(2007/10/03)
CYCLOADDITION OF DICLOROKETENE WITH FUNCTIONALIZED CYCLOALKENES. SYNTHESIS OF BICYCLOOCTANONE-3-YL DERIVATIVES AND OF 3,4-DICARBOXYMETHOXY-1-METHYLBICYCLOOCTAN-7-ONE
Dichloroketene reacts with some cycloalkenes in wich an ester function is in homoallylic or in an even more remote position with respect to sp2 carbon atoms.In fact acetate and benzoate of 3,5,5-trimethylcyclohex-3-en-1-ol and 1,2-dicarbomethoxy-4-methyl-cyclohex-4-ene undergo 2+2 cycloaddition of dichloroketene to produce the corresponding bicyclooctanone derivatives in 60-65percent yield.In the latter case the process occurs regiospecifically to give 3,4-dicarboxymethoxy-1-methylbicyclooctan-7-one as product after dechlorination.The Hassner zinc dehalogenation method of generating dichloroketene is the best procedure.
STEREOCHIMIE-LII. CONTROLE ORBITALAIRE DE LA STEREOCHIMIE DES REACTIONS-III EFFETS DES GROUPES β-FLUORO ET β-CYANO SUR LA STEREOCHIMIE ET LA CINETIQUE DE LA REDUCTION DE CYCLOHEXANONES PAR LE TRITERTIOBUTOXYALUMINOHYDRURE DE LITHIUM
The respective influences of β-fluoro and β-cyano groups on the reduction of ketones by Li(t-BuO)3AlH on the stereoselectivities of the reduction with and without added cryptands, and with and without added alkyl fluoride and nitrile, were compared with ab initio calculations using the frontier orbitals of analogous carbonyl compounds to give energy values