Joerg Pietruszka

Total synthesis of the protein phosphatase inhibitor okadaic acid

The total synthesis of the protein phosphatase inhibitor okadaic acid 1 is reported using a convergent coupling strategy of three components, all of which may be prepared using chemistry developed in our laboratories.

Enantiomerically pure cyclopropylboronic esters: auxiliary- versus substrate-control

Stable, enantiomerically pure cyclopropylboronic esters are synthesized from alkynes by a hydroboration–cyclopropanation sequence. The direct hydroboration—utilizing 1,3,2-dioxaborolane 4—is most convenient, however, with more functionalized side-chains it failed to give the desired intermediates. Using the more reactive dicyclohexylborane, followed by oxidation and transesterification, is a good alternative one-pot conversion. Cyclopropanations were performed either following a Simmons–Smith protocol or with diazomethane–palladium(II) acetate. The influence on the diastereoselectivity of the auxiliary 1 is compared with the influence of an additional stereogenic center in the side-chain.

Enantiomerically pure 1,3,2-dioxaborolanes: new reagents for the hydroboration of alkynes

Stable, enantiomerically pure alkenylboronic esters 2 are conveniently prepared by direct hydroboration employing the new 1,3,2-dioxaborolane 4; their highly diastereoselective cyclopropanation can be achieved.