Cyclopropylboronic esters

Chen, H. Deng, M.-Z. A novel Suzuki-type cross-coupling reaction of cyclopropylboronic esters with benzyl bromides./. Chem. Soc. Perkin Trans. 1 2000, 1609-1613. 

The methods for stereocontrolled synthesis of cyclopropylboronic esters have been studied (Scheme 29). The palladium-catalyzed reaction of diazoalkanes (method A), Simmons-Smith reaction (method B), or asymmetric Simmons-Smith reaction using chiral diamines such as 270 (method C) for chiral or achiral 1-alkenylboronic esters... 

Pietruszka, J., and With A., Enantiomerically pure cyclopropylboronic esters. Auxiliary- versus substrate-control, J. Chem. Soc., Perkin Trans. 1, 4293, 2000. 

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. 

Interesting compounds, such as cyclopropylboronic acids and esters which are otherwise not easily accessible due to the apparent lack of convenient and versatile syntheses, can now be prepared by simple cyclopropanation with diazomethane. The carbene transfer to substituted and functionalized alkenes also takes place smoothly in the presence of palladium(II) acetate. Several 1-alkenylboronic acid esters 9 were converted to cyclopropylboronic acid esters 10 using this method. ... 

Suzuki coupling. Unsymmetrical biaryls are prepared by Suzuki coupling at ambient temperature in iV,lV-dimethylacetamide in the presence of TIOH. Arylcyclopropanes are most amenable to assembly by a Suzuki coupling, due to the ready availability of cyclopropylboronic acids and esters. 

Alkenylboronic acids and esters are also very useful substrates (Equation 71, Figure 1.38) [405], in particular to access substituted olefins and dienyl moieties commonly encountered in several classes of bioactive natural products [282, 406]. To this end, Kishi and co-workers examined the influence of the base, and developed an optimal variant using thallium hydroxide [281]. Recently, allylic alcohols were found to couple directly with alkyl and alkenyl boronic acids without the aid of a base [407]. In rare cases, the Suzuki reaction has been applied to the use of alkylboronic acids [296, 408], including cyclopropylboronic acids [409]. Hitherto notorious for their tendency to undergo [3-hydride elimination, alkyl bromides are now suitable as electrophiles under carefully optimized conditions that even allow Csp -Csp couplings with alkylboronic acids (Equation 72) [410]. The Suzuki reaction has also been applied very successfully in solid-phase chemistry and combinatorial library synthesis [411]. It has been applied industrially [412], especially in medicinal chemistry, e.g. in the production of the antihypertensive drug losartan [195]. 

Further transformations of cyclopropylboronates by creation of a new carbon-carbon or carbon-oxygen bond have been largely developed, as well as the modification of the side-chain in the presence of the boronic ester functionality [46]. 

SCHEME 13.19. Reaction of cyclopropylboronic acids with organic halides and cross-coupling of acyclic secondary alkylbor-onic esters with aryl iodides. 

---