The chirality transfer on the P-tetronic acid templates has been examined via highly diastereoselective alkylation or the Michael reaction at the aposition of the acids.Synthetic utility of this transfer procedure was demonstrated by the formal synthesis of (+)-cassiol and enantiodivergent synthesis of 0-methyljoubertiamine.P-Teuonic acids (1) are one of the attractive building blocks for the syntheses of several classes of natural products2due to the presence of multifunctionality in the molecule.Previously, we have demonstrated the efficient preparation of 1 (R1, R2 = H),3 and investigated the reactivity of its congeners at the aposition?However, most fundamental studies in the alkylation on the system have been reported only to a small extent.5Recently, we reponed our preliminary results on the selective allylation at the aposition of optically active a-methyltemnic acids via direct allylation and the Claisen rearrangement of allyl teuonates concomitantly formed in the preceding direct a1l~lation.6In this paper, we wish to repon a full account of detail examination on the alkylation of optically active a,y-disubstituted teuonic acids and the Michael reaction as another cirbon-chain homologation at the a-position.As a synthetic utility of this method, formal synthesis of (+)-cassio17 and enantiodivergent synthesis of 0-methyljoubemamine8 were accomplished.The starting optically active a,y-disubstituted temnic acids ( l a ) -( l e ) were prepared from commercially available methyl lactate, L-phenylalanine and L-valine by employing the intramolecular Reformatsky reaction9 as shown below.
Three new rearranged vibsane-type diterpenes, neovibsanin F (1), 14-epi-neovibsanin F (2), and 14-epi-18-oxoneovibsanin F (3), have been isolated from the leaves of Viburnum suspensum, and their structures were elucidated on the basis of spectroscopic data and comparison with those of previously reported vibsane-type diterpenes.
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