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One hundred years of helicene chemistry. Part 2: stereoselective syntheses and chiral separations of carbohelicenes, J. Am. Chem. Soc, vol.42, issue.2, pp.12373-12376, 2010. ,
A Straightforward route to helically chiral N-heteroaromatic compounds: practical synthesis of racemic 1,14-diaza[5]helicene and optically pure 1-and 2-aza[6]helicenes, Angew. Chem. Int. Ed, vol.139, issue.3, pp.9111-9114, 2002. ,
Selectivity in the thermal and photochemical fragmentation of the cycloadduct from benzyne and a mesoionic thiazol-4one, For other pioniring reports see: b), vol.4, pp.621-621, 1968. ,
Cycloaddition-extrusion reactions of five-membered mesoionic compounds with benzyne: prepartion of benz[c]azole and benzo[c]thiophen derivatives, J. Chem. Soc., Perkin Trans. 1, vol.6, issue.13, pp.2234-2237, 1974. ,
) The measured racemization barrier for pyrazolo[7]-helicene 10a was found to be 32.7 kcal/mol. This value is in agreement with the calculated racemization energy barrier for 10a: 31.6 kcal/mol. See ref 11 for details. (17) The degree of CPL is given by the luminescence dissymmetry ratio, glum(?) = 2?I/I = 2(IL-IR)/(IL+IR), where IL and IR refer, helicene 9a is not configurationally stable at room temperature, vol.76, pp.188-191, 1922. ,
Straightforward access to mono-and bis-cycloplatinated helicenes displaying circularly polarized phosphorescence by using crystallization resolution methods, Angew. Chem. Int. Ed, vol.50, issue.20, pp.4242-4253, 1915. ,
Frontier molecular orbitals of 1,3 dipoles and dipolarophiles, J. Am ,
On the problem of regioselectivity in the 1,3-dipolar cycloaddition reaction of munchnones and sydnones with acetylenic dipolarophiles, J. Am. Chem. Soc, vol.95, issue.21, pp.786-791, 1973. ,
) Noteworthy, in presence of unsymmetric cyclooctynes, sydnones have been reported deliver a 1 to 1 mixture of regioisomers: Narayanam, J. Am. Chem. Soc, vol.137, issue.22, pp.1257-1261, 2015. ,
) The nature of pyrazoles 11a and 11b was unambiguously established by NOE and X-ray crystallography (see SI for details). (26) In all cases, the reactions are HOMO (sydnone)-LUMO (aryne) controlled. See Supporting Information for details. (27) For a review on aromatic interactions as control elements in stereoselective reactions, see: Krenske, E. H.; Houk, K. N. Aromatic interactions as control elements in stereoselective organic reactions, Angew. Chem. Int. Ed, vol.132, issue.25, pp.10070-10086, 2010. ,