[123]Tetramantane: Parent of a New Family of σ-Helicenes

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Abstract
We present a new type of σ-helical structure based on a diamondoid (nanodiamond) framework, C2-symmetric [123]tetramantane, whose (+) and (−) isomers could be enantioseparated by HPLC techniques. Bromination of the enantiopure hydrocarbon led to the isolation of (+)-7-bromo-[123]tetramantane, which could be crystallized and subjected to X-ray structure analysis. Using the anomalous dispersion, we have identified this compound as the P isomer for the hydrocarbon moiety. Experimental and computed optical rotatory dispersion (ORD) and vibrational circular dichroism (VCD) spectra independently and in agreement with the X-ray structure analysis gave M-(−) as the configuration of the second eluted parent hydrocarbon isomer.