Matched Coupling of Propargylic Carbonates with Cyclopropanols

Abstract

The ring opening-coupling reaction of cyclopropanols with propargylic carbonates affording synthetically attractive allenyl ketones has been developed. The mechanism involves the ligand-exchange reaction of in situ formed allenyl palladium methoxide with cyclopropanols followed by carbon-carbon bond cleavage and reductive elimination. The reactions proceeded smoothly under mild reaction conditions with Pd(0)/XPhos catalysis in the absence of any external base and displayed a wide scope and application to a steroidal skeleton. The efficiency of chirality transfer and synthetic utility of the allene products have also been demonstrated.

Modern Developments in the Chemistry of Homoenolates

“…Selected examples of palladium‐catalyzed couplings that have been applied to simple (i.e., non‐acetal‐type) cyclopropanols are shown in Scheme . These include arylation,, acylation, benzylation, and allenylation reactions …”

Pd-catalyzed reactions of cyclopropanols, cyclobutanols and cyclobutenols

“…41). 40 Interestingly, optically active propargylic carbonates provided the allene with high chirality transfer (Eq. 42).…”

Metal-Catalyzed Transformations of Cyclopropanols via Homoenolates

“…In 2018, Ma and coworkers reported Pd-catalyzed ringopening allenylation of cyclopropanols with propagylic carbonates (Scheme 34a). 55 The reaction between 1-substituted cyclopropanols and secondary or tertiary propargylic carbonates was promoted by a catalytic system comprised of Pd(dba)2 and XPhos in the absence of an external base, afforded β-allenyl ketones in moderate to good yields. Central-to-axial chirality transfer was observed in the reaction of optically active propargylic carbonates.…”