The first total synthesis of clavaminol A and C, (2R,3S)-2-amino-3-alkanols from the Mediterranean ascidian Clavelina phlegraea has been achieved in 29% overall yield. The key step involved a palladium(II)-catalysed directed Overman rearrangement to create the C-N bond and install the erythro configuration while a one-pot, tributyltin hydride-mediated reduction allowed simultaneous formation of the methyl side-chain and N-acetyl group. Similarly, the first total synthesis of clavaminol H was completed in 48% overall yield using an approach that also provided the cytotoxic des-acetyl analogue.
A highly efficient one-pot multistep process involving an asymmetric Pd(II)-catalyzed Overman rearrangement and a Ru(II)-catalyzed ring-closing metathesis reaction has been developed for the preparation of (R)- or (S)-aminocyclopenta-2-enes. The rapid strategy employed and the relatively mild conditions of the one-pot process allowed the multigram synthesis of the carbocycles in high enantiomeric excess (92% ee). The synthetic utility of these compounds was demonstrated by the stereoselective incorporation of hydroxyl groups, generating cis-4- and cis-5-aminocyclopenta-2-en-1-ols, important building blocks for medicinal chemistry.
Two
variations of the Overman rearrangement have been developed
for the highly selective synthesis of anti-vicinal
amino alcohol natural products. A MOM ether-directed palladium(II)-catalyzed
rearrangement of an allylic trichloroacetimidate was used as the key
step for the preparation of the protein kinase C inhibitor d-erythro-sphinganine and the antitumor agent (+)-spisulosine,
whereas the Overman rearrangement of chiral allylic trichloroacetimidates
generated by the asymmetric reduction of an α,β-unsaturated
methyl ketone allowed rapid access both to d-ribo-phytosphingosine and l-arabino-phytosphingosine.
A stereoselective synthesis of (+)-physoperuvine, a tropane alkaloid from Physalis peruviana Linne has been developed using a one-pot tandem aza-Claisen rearrangement and ring closing metathesis reaction to form the key amino-substituted cycloheptene ring.
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