Chirality (helicity, planar chirality)
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Regioselective Complexation of [2.2]Metacyclophanes with TriamminetricarbonylchromiumThe new [2.2]phanes 12, 13, 15, and 17 have been prepared. For the preparation of the known phane 16 a new route has been developed which leads to better yields and includes an interesting reduction with Raney nickel of the naphthalene ring of 15 to a tetrahydronaphthalene ring (→17). The phanes react regioselectively with triamminetricarbonylchromium, which results exclusively in the complexation of the sterically less hindered benzene ring. The bis(tricarbonylchromium) complexes of 18 and 17 were available in good yields, when two equivalents of the precursor of the tricarbonylchromium group were used. 18a was lithiated at -78°C, and the lithiated complexes were trapped with either chlorotrimethylsilane or ethyl chloroformate to yield 4- and 5-substituted products in a ratio of 4:5. Ten X-ray structures, including those of six transition metal π complexes, which were investigated and compared under the aspect of steric interactions between the tricarbonylchromium group and the substituent at the arene ring, are discussed. Interestingly, the tricarbonylchromium group shows no noticable effect on the boat-like deformation of the benzene ring in [2.2]metacyclophanes. A new definition of the “angles of helicity” in helical [2.2]phanes is introduced.
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