16914-68-4Relevant articles and documents
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Bernstein,W.J. et al.
, p. 494 - 498 (1972)
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Origin of the Preferential Formation of Helicenes in Mallory Photocyclizations. Temperature as a Tool to Influence Reaction Regiochemistry
Weber,Clennan
, p. 817 - 830 (2019)
The regiochemistry of four bis-Mallory photocyclization substrates has been examined from experimental and computational perspectives. Formation of all three possible regioisomers was only observed in the reaction of one of the substrates. In the other three substrates, only the two C2-symmetric products, but not the C1 product, were formed. In the three reactions that only formed two products, the photocyclization temperature could be used to select for exclusive formation of one or the other regioisomer. The use of temperature to select between two regioisomers also worked in the photocyclization of the substrate that formed three products. However, no temperature was located for exclusive formation of the third component, one of the C2-symmetric products, which always formed alongside either one or both of its regioisomers. B3LYP/6-311+G(2d,p) calculations were used to determine the energies of all of the dihydrophenanthrene (DHP), tetrahydrophenanthrene (THP), and mono-Mallory photocyclization intermediates. The oscillator strengths of the DHP precursors to the helicene products were a factor of 4.8-9.2 smaller than those of competitively formed DHPs. This observation suggests that establishment of a photostationary state is responsible for the preferential formation of helicenes that has been observed as a unique and useful feature of many Mallory photocyclizations.
Modified synthesis of heftahelicene and its resolution into single enantiomers
Alexandrova, Zuzana,Sehnal, Petr,Stara, Irena G.,Stary, Ivo,Saman, David,Urquhart, Stephen G.,Otero, Edwige
, p. 1256 - 1264 (2006)
A practical synthesis of racemic heptahelicene has been develeped being based on key [2+2+2] cycloisomerization of bis[2-(but-3-yn-1-yl)-1-naphthyl] acetylene under CpCo(CO)2/PPh3 or CpCo(C2H 4)2 catalysis. The application of the Ni(COd)2 catalyst with (-)-(Sa)-(2′-methoxy-1,1′-binaphthalen-2- yl)diphenylphosphane resulted in enantioselective triyne cyclization to provide (+)-7,8,11,12-tetrahydroheptahelicene in 40% ee. Optically pure (-)-(M)- and optically highly enriched (+)-(P)-heptahelicene were obtained on a milligram scale by resolution of racemate by chiral HPLC on a semipreparative Whelk-O1 column.
Expeditious synthesis of helicenes using an improved protocol of photocyclodehydrogenation of stilbenes
Talele, Harish R.,Chaudhary, Anju R.,Patel, Parthiv R.,Bedekar, Ashutosh V.
experimental part, p. 15 - 37 (2011/06/19)
An improved procedure has been developed for photodehydrocyclization of stilbenes for the synthesis of phenanthrenes and helicenes. This procedure involves the use of THF as a scavenger of hydriodic acid produced during iodine mediated photodehydrocyclization. The use of THF is advantageous due to its higher boiling point, lower cost and easy availability as compared to propylene oxide. The method is applied to synthesize a number of phenanthrenes and helicenes. ARKAT-USA, Inc.
