Substrate-controlled highly diastereoselective synthesis of primary and secondary diorganozinc reagents by hydroboration/boron-zinc exchange sequence.

The scope of substrate-controlled diastereoselective hydroborations can be considerably enhanced by a boron-zinc exchange reaction, providing organozinc derivatives that react with a broad range of electrophiles. Even normally unreactive boronic esters, obtained by Rh-catalyzed hydroboration with catecholborane, react readily with iPr2Zn providing the corresponding zinc reagents in high diastereoselectivity.

Highly anti-selective SN2' substitutions of chiral cyclic 2-iodo-allylic alcohol derivatives with mixed zinc-copper reagents.

[reaction: see text] Functionalized allylic electrophilic reagents such as chiral 2-iodo-1-cyclohexenyl and -cyclopentenyl phosphates undergo highly stereoselective anti-S(N)2'-allylic substitution reactions with a wide range of organozinc reagents (R(2)Zn and RZnI) leading to chiral products with a transfer of the chiral information >95%. The use of functionalized organozinc iodides allows preparation of the bicyclic enones 8 and 9 in >or=93% ee.

Diastereoselective reduction of alkenylboronic esters as a new method for controlling the stereochemistry of up to three adjacent centers in cyclic and acyclic molecules.

[reaction: see text] cis-Boronates are readily available via a diastereoselective Pd-catalyzed reduction of tetrasubstituted alkenylboronic esters using H2. Applying the reaction conditions presented to unsaturated open-chain boronic esters allows the stereochemistry of up to three adjacent centers to be controlled.