page_title: Ladderane
section_title: Dimerization of polyene precursors
hierarchical_section_title: Ladderane / Synthesis / Dimerization of polyene precursors
caption_attribution_description: English: Synthesis of ladderanes through the dimerization of polyene precursors.
context_page_description: In chemistry, a ladderane is an organic molecule containing two or more fused cyclobutane rings. The name arises from the resemblance of a series of fused cyclobutane rings to a ladder. Numerous synthetic approaches have been developed for the synthesis of ladderane compounds of various lengths. The mechanisms often involve [2 + 2] photocycloadditions, a useful reaction for creating strained 4-membered rings. Naturally occurring ladderanes have been identified as major components of the anammoxosome membrane of the anammox bacteria Planctomycetes.
context_section_description: In these reactions, ladderanes are formed from multiple [2 + 2] photocycloaddiitions between the double bonds of two polyenes. A complication that arises from this approach is the reaction of the precursors through alternative, more favorable photoexcitation routes. These side reactions are prevented by the addition of a chemical spacer unit that holds the two polyenes parallel to each other, only allowing [2 + 2] cycloadditions to occur.
  A common spacer used in these reactions is the [2.2]paracyclophane system. This is sufficiently rigid and can hold the polyene tails in close enough proximity for the cycloadditions to occur.
  MacGillivray and colleagues have demonstrated that a supramolecular approach to covalent synthesis in the organized, solvent-free environment of the solid state can provide a solution to the problem of organizing two polyenes for an intramolecular reaction to give a ladderane. Specifically, by taking an approach to control reactivity in solids by using molecules that serve as linear templates, they have demonstrated the utility of cocrystallization of resorcinol (1,3-benzenediol), or a derivative, with an all-trans-bis(4-pyridyl)poly-m-ene (4-pyr-poly-m-ene) produces a four-component molecular assembly, 2(resorcinol)·2(4-pyr-poly-m-ene), in which each resorcinol preorganizes, through two O—H···N hydrogen-bonding interactions, two poly-m-enes for [2+2] photoaddition. The two polyenes are positioned by the templates such that the C=C bonds of the olefins lie parallel and separated by < 4.2 Å, a position suitable for the photoreaction. UV irradiation of the solid produces the targeted [n]ladderane, with the C=C bonds reacting to form the fused cyclobutane framework. Broadband UV-irradiation of two such hydrogen-bonded, four-component supramolecular assemblies furnishes the corresponding ladderanes stereospecifically and in quantitative yield in gram quantities.
caption: Synthesis of ladderanes through the dimerization of polyene precursors
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