Serial [5+2]/[4+2] Cycloadditions: Facile, Preparative, Multi-Component Syntheses of Polycyclic Compounds from Simple, Readily Available Starting Materials

Transition Metal-Catalyzed Selective Carbon-Carbon Bond Cleavage of Vinylcyclopropanes in Cycloaddition Reactions

In this review, transition metal-catalyzed methodologies and applications that exploit C-C bond cleavage of vinylcyclopropanes (VCPs) are summarized with a focus on cycloaddition and related addition reactions. Transition metals, including palladium, nickel, iron, ruthenium, rhodium, cobalt, and iridium, can catalyze the cleavage of C-C bonds in activated or nonactivated VCPs. Additionally, these bond-breaking reactions can occur as intra- or intermolecular processes. The properties of activated and nonactivated VCPs are discussed in the Introduction. Various transition metal-catalyzed cycloaddition and addition reactions involving the cleavage of C-C bonds in activated VCPs are then discussed in the next chapter. The transition metal-catalyzed cycloadditions involving the cleavage of C-C in nonactivated VCPs are summarized in the following chapter. Finally, challenges and potential opportunities are outlined in the last chapter.

Ruthenium-catalyzed reactions--a treasure trove of atom-economic transformations

The demand for new chemicals spanning the fields of health care to materials science combined with the pressure to produce these substances in an environmentally benign fashion pose great challenges to the synthetic chemical community. The maximization of synthetic efficiency by the conversion of simple building blocks into complex targets remains a fundamental goal. In this context, ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy. These complexes often exhibit unusual reactivity. Careful consideration of the mechanistic underpinnings of the transformations can lead to the design of new reactions and the discovery of new reactivity.

Syntheses of Seven-Membered Rings: Ruthenium-Catalyzed Intramolecular [5+2] Cycloadditions

The Ru-catalyzed intramolecular [5+2] cycloaddition of cyclopropylenynes is investigated with respect to the regio- and diastereoselectivity as well as the functional group compatibility of the reaction. Evidence for the mechanism as occurring through a ruthenacyclopentene intermediate is elucidated from 1) the study of the diastereoselectivity of the cycloaddition; 2) the effect of variation of substituents on the regioselectivity of cyclopropyl bond cleavage in 1,2-trans- and 1,2-cis-disubstituted cyclopropanes and 3) examples that clearly do not involve ruthenacyclohexene as intermediates as products still incorporate the cyclopropyl moiety. The scope and limitations of the Ru-catalyzed cycloaddition are discussed and compared with the Rh-catalyzed reaction. The potential power of this methodology towards natural product total synthesis is demonstrated by the formation of several polycyclic systems with the chosen reaction conditions and readily available cyclopropylenyne substrates.