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Aromatic Helicenes
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
The highly exergonic transition metal-catalyzed intramolecular [2 + 2 + 2] cycloisomerization of aromatic triynes (and related cyanodiynes or ynedinitriles) represents a new paradigm for the highly versatile nonphotochemical synthesis of helicenes, tetrahydrohelicenes, dibenzohelicenes, heterohelicenes, partially hydrogenated helicenes, helicene-like compounds and their functionalized derivatives (Stará et al., 1998; Teplý et al., 2002; Míšek et al., 2008) (Figure 4.13). The key cyclization can be catalyzed by various metal complexes (mostly by CoI, Ni0, RhI), allows for constructing three cycles of the helicene skeleton in a single operation (in contrast to other concurrent processes), is highly tolerant to a wide range of functional groups and can be done in an asymmetric fashion. The starting triynes (and their heteroanalogues) are usually easily accessible. The synthetic methodology originally developed by Stará et al. (1998) has recently attracted a considerable attention as other groups also recognized its synthetic potential such as Vollhardt et al. (Han et al., 2002a), Teplý et al. (Adriaenssens et al., 2011), Tanaka et al. (Sawada et al., 2012), Shibata et al. (Shibata et al., 2012), Carbery et al. (Crittall et al., 2011), Diederich et al. (Roose et al., 2013), Marinetti et al. (Aillard et al., 2014) and others. Discouraging results might occasionally be obtained if the key triyne intermediate tends to polymerize and if the starting di- and trisubstituted aromatic building blocks are difficult to obtain. It is worth noting that dibenzo[5]-, dibenzo[6]- and dibenzo[7]helicenes as well as their functionalized derivatives and heterocyclic analogues are easily accessible (optionally on a multigram scale) by employing a short sequence of reliable processes such as Sonogashira coupling, Suzuki–Miyaura coupling and [2 + 2 + 2] alkyne cycloisomerization as reported by Stará, Starý et al. (Jančařík et al., 2013) (Figure 4.14). Dibenzohelicenes have an advantage over the parent helicenes because of the simplicity of their non-photochemical preparation, and therefore, they have the potential to mimic or even substitute parent helicenes in envisaged applications.
Synthesis of six- and seven-membered and larger heterocylces using Au and Ag catalysts
Published in Inorganic and Nano-Metal Chemistry, 2018
The rhodium-catalyzed reaction of diazo ketones with alkynes produced alkenyl rhodium carbenoids.[15h-p] An intramolecular trapping with alkene of vinylogous acceptor-substituted carbenoids occurred,[15q-r] in turn carbenoids were prepared by ring opening of cyclopropenyl ketones. However, cycloisomerization of appropriately substituted cyclopropene-enes that occurs through intramolecular cyclopropanation of the remote olefin in the presence of transition-metal catalyst remained highly unexplored. One of the first example of such reaction is rearrangement of 3-allyl-1,2-diphenylcyclopropene into substituted bicyclo-[3.1.0]hex-2-ene with Ag catalyst.[15s-t] The 3-aza- or 3-oxabicyclo[4.1.0]heptanes I were obtained in excellent diastereoselectivities and in high yields by cycloisomerization of cyclopropene-enes in the presence of Au catalyst.[15u-z,16a-c] Since the [4.1.0]bicycloheptan-2-ones were produced when isopropylidene group underwent ozonolysis,[16d] this method compared the copper-catalyzed intramolecular cyclopropanation of diazoalkenyl ketones[16e] in terms of diastereoselectivity and efficiency (Scheme 8).
Copper-assisted synthesis of five-membered O-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Yamini Verma, Neha Ahlawat, Pooja Grewal, Pranshu Bhardwaj, Nirmala Kumari Jangid
Nefedov[22] reported the cycloisomerization of cyclopropenes to afford furans in the presence of transition metal catalyst. The vinylcarbene was yielded via a small cycle cleavage in ester with copper(I) salts. The vinylcyclopropane adduct was formed by trapping of carbenoid species with a norbornadiene double bond (Scheme 4).[23]