Dioxaborolane auxiliaries

Roush and co-workers have shown that the nature of the substituents on the dioxaborolane auxiliary profoundly affects the rate and enantioselectivity of the allylboration reaction reagents with ester substituents are far more reactive and more selective than reagents with alkyl substituents. The enantioselectivity of reagents 1-3 is thought to arise more from electronic attraction and repusion than from steric hindrance. 

Use as a Chiral Auxiliary Synthesis of Cyclopropylboronic Acids. The chiral dioxaborolane unit can also be used as an effective chiral auxiliary in the synthesis of enantiomerically enriched cyclopropylboronic acids. For example, 1-alkenylboronic esters bearing the tetramethyltartramide group undergo diastereoselec-tive cyclopropanations to afford the cyclopropylboronic acid (eq 11). These products can be used for in situ Suzuki coupling reactions or can be oxidized to produce 2-substituted cyclopropanols. 

---