The First Enantiomerically Pure [n]Triangulanes and Analogues: σ-[n]Helicenes with Remarkable Features

Three-Membered-Ring-Based Molecular Architectures

“…312 According to this, the number of stereoisomers grows rapidly with an increasing number of three-membered rings, and many of the diastereomers of higher [n]triangulanes (n g 4) 55% and 52% yield, respectively, after gas chromatographic separation in the last step (Scheme 69), corresponding to a 5% and 9%, respectively, overall yield from the methylene[3]triangulanes (R)-445 and (S)-445, respectively, with an enantiomeric excess of g94% for both. 316 However, because of the rapidly growing number of possible stereoisomers of these [n]triangulanes with increasing n, for example, the family of [9]triangulanes consists of 4 meso-diastereomers and 16 pairs of enantiomers, 312 [3]triangulane (dispiro[2.0.2.1]heptane) exhibits virtually a linear dependence on the number of the rings with a regression line ∆[R] ) 223.32 -7.72n and a correlation coefficient r ) 0.999. The extrapolation of this line intersects the baseline at n ) 29, which means that the specific rotation, normalized with respect to the number (n -3) of threemembered rings added to the achiral [3]triangulane, for higher enantiomerically pure helical [n]triangulanes (n g 29) would not increase any more.…”

New Structurally Interesting Cyclopropane Derivatives: A World of Wonders and Surprises

“…Among them, the linear triangulanes with more than three spiro-linked cyclopropane units display an interesting stereochemical phenomenon in that they are chiral, but with stereogenic centers that have four different alkyl substituents only [6]. This stimulated us to prepare the first [n]triangulanes in enantiomerically pure form and investigate their properties (Scheme 1) [7,8].…”

“…Fortunately, three of the four diastereomeric ethyl [4]triangulanecarboxylates obtained by rhodium-catalyzed cyclopropanation with ethyl diazoacetate of either one of the enantiomerically pure 1-methylene [3]triangulanes could be distilled off the remaining one through a high-performance concentric tube column, and the residue in the distillation flask proved-by X-ray crystallography-to be one of two diastereomers that could be used to proceed further (Scheme 2) [8].…”

“…The crystal structures of the enantiomerically pure (P)-enantiomer and of the racemic [5]triangulane were both determined by X-ray diffraction. While the molecular structures were-of course-identical, the crystal packing for the enantiomerically pure and the racemic compound were found to be significantly different [8]. Although the enantiomeric purity for the (M)-enantiomer was of the same order as that for the (P)-enantiomer, the specific rotation was about 11 % [7,8].…”

1,4‐Dimethylenespiropentane: A Unique Model System for Studying Fermi Resonance in Raman Optical Activity

“…For small molecules, and in the absence of specific interactions in the condensed phase, agreement between computed and measured Raman and ROA spectra can actually be astounding. [1] 1,4-Dimethylenespiropentane [8] looks, at the outset, like another model compound well-suited for confirming the reliability of the ab initio computation of vibrational optical activity. The C 2 -symmetric rigid molecule has no conformational freedom, and strong, specific interactions in the liquid phase are not expected for a pure hydrocarbon compound.…”