Conformational Studies of Selectively Methylated [2.2](1,3)(1,4)Cyclophanes. Steric Effects in the Relative Conformational Ground States

Attempt Towards Syn-Benzothiazolophane: Synthesis and Conformational Study of SYN-DITHIA-[3.3](2,6) Benzothiazolophane

“…The internal aromatic C-7 proton appeared upfield at 6.65 δ as a singlet, whereas, C-4 and C-5 aryl protons are observed as a doublet each at 7.55 δ (8Hz) and 7.22 δ (8Hz), respectively. Space filling CPK model also indicated the presence of a constricted cavity in 3 which appears too small to accommodate the orthogonal transition state during the ring rotation (23). The observed conformational immobility of 3 may be attributed to a large steric barrier imposed together by C-7 internal hydrogen and the bulky 'S' atom of the benzothiazole nuclei to the ring flipping process.…”

Breaking paracyclophane: the unexpected formation of non-symmetric disubstituted nitro[2.2]metaparacyclophanes

“…But the odd one out of the simple [2.2]cyclophane series appears to be [2.2]metaparacyclophane (3). Compared to the other two isomers, there has been scant research [18][19][20][21][22][23] conducted on this framework. A search for the word `[2.2]metacyclophane*` in SciFinder gives 315 hits (192 hits on Web of Science) while a search for word ` [2.2]metaparacyclophane*ò nly has 69 hits on Scifinder (and 35 for Web of Science; searches were conducted 29th September 2020).…”