Propellanes—From a Chemical Curiosity to “Explosive” Materials and Natural Products

Abstract

Propellanes are a unique class of compounds currently consisting of well over 10 000 representatives, all featuring two more or less inverted tetrahedral carbon atoms that are common to three bridging rings. The central single bond between the two bridgeheads is significantly weakened in the smaller entities, which leads to unusual reactivities of these structurally interesting propeller-like molecules. This Review highlights the synthesis of such propellanes and their occurrence in material sciences, natural products, and medicinal chemistry. The conversion of [1.1.1]propellane into bridgehead derivatives of bicyclo[1.1.1]pentane, including oligomers and polymers with bicyclo[1.1.1]penta-1,3-diyl repeat units, is also featured. A selection of natural products with larger propellane subunits are discussed in detail. Heteropropellanes and inorganic propellanes are also addressed. The historical background is touched in brief to show the pioneering work of David Ginsburg, Günther Snatzke, Kenneth B. Wiberg, Günter Szeimies, and others.

Nonconjugated Hydrocarbons as Rigid‐Linear Motifs: Isosteres for Material Sciences and Bioorganic and Medicinal Chemistry

“…The inverted carbon geometry of the bridgehead–bridgehead bond, no matter of the actual bond character itself–which most likely will stay unrevealed–still tests current theoretical calculations of energy and bond lengths (Table ) . Further information about BCP and related propellanes can be found in other very comprehensive reviews …”

“…BCP was also utilized as a rigid linker to study FRET between the fluorophore 1,5‐dimethoxy‐9,10‐di(phenylethynyl)anthracene (donor) and different substituted thiophene acceptor units 167 . Its short C 1 –C 3 distance makes it a unique linker, allowing two conjugated chromophores to be in close proximity while not allowing any significant π‐conjugation.…”

“…Over the years, linear linking has been a classic field of para ‐substituted benzenes and alkynes, due to the plethora of well‐established cross‐coupling reactions . Recently however, certain other hydrocarbons, such as cubane or bicyclo[1.1.1]pentane (BCP) have begun to draw attention due to their remarkable properties . Besides these highly strained, rather unusual hydrocarbons more common moieties are in use, such as bicyclo[2.2.2]octane (BCO) and triptycene (Figure ).…”

Design and Synthesis of Polycycles, Heterocycles, and Macrocycles via Strategic Utilization of Ring‐Closing Metathesis

“…The smallest propellane, for example, [1.1.1]propellane was found to be highly strained and unstable molecule. The bicyclo[1.1.1]pentyl units produced from [1.1.1]propellane are the key precursors used in material sciences such as polymer chemistry, nanochemistry, and design of liquid crystals . In spite of the availability of several useful approaches to assemble propellane skeleton, the RCM protocol has been proved to be a powerful method .…”

Selectivity in Ring‐Closing Metathesis: Synthesis of Propellanes and Angular Aza‐tricycles

“…[5] For example, synthesis of cis-syn-cis triquinane [6] over the propellanes, [7] tandem ring-closing metathesis (RCM) [8] followed by aromatization, chemo-selective self-metathesis [9] and crossmetathesis (CM) reactions. The propellanes [11] and angular aza-tricycles are generally found as core structural units in biologically active natural products [12] (Figure 1) such as kopsia indole alkaloids (e. g., fruticosine and kopsanone) [13] and erythrina alkaloids [14] (e. g., isococculidine and b-erythrodine). Fischer indolization and Grignard reactions are used as key steps to prepare the substrates required for RCM.…”