Preparation of Strained Axially Chiral (1,5)Naphthalenophanes by Photo-dehydro-Diels−Alder Reaction

Abstract

The preparation of 10 (1,5)naphthalenophanes (10a-j) by photo-dehydro-Diels-Alder (PDDA) reaction is described. Owing to hindered rotation around the biaryl axis, compounds 10 are axially chiral and the separation of enantiomers by chiral HPLC was demonstrated in three cases (10a,b,e). The absolute configuration of the isolated enantiomers could be unambiguously determined by comparison of calculated and measured circular dichroism (CD) spectra. Furthermore, we analyzed ring strain phenomena of (1,5)naphthalenophanes 10. Depending on the length of the linker units, one can distinguish three classes of naphthalenophanes. Compounds 10a-c are highly strained (E(STR) = 7-31 kcal/mol), and the strain is caused by small bond angles in the linker unit and deformation of the naphthalene moiety. Another type of strain is observed if the linker unit becomes relatively long (10g,h) originating from transannular interactions and is comparable with the well-known strain of medium sized rings. The naphthalenophanes 10d-f with a linker length of 10-14 atoms are only marginally strained. To clearly discriminate the different sources of strain, we defined two geometrical parameters (average central dihedral angle δ(C) and naphthalene thickness D(N)) and demonstrated that they are well-suited to indicate naphthalene deformation of our naphthalenophanes 10 as well as of ten model naphthalenophanes (I-X) with different linker lengths and linking positions.

Asymmetric Synthesis of (1,5)Naphthalenophanes by Dehydro‐Diels–Alder Reaction

“…Recently, we reported on the photochemical preparation of, at least in part, highly strained (1,5)naphthalenophanes by intramolecular PDDA reaction 5e. In this work, the structure of the reactants rested upon linkage of two molecules of 3‐(2‐[3‐oxo‐1‐butynyl]phenyl)propionic acid ( 1 ) by esterification with various diols.…”

Recent Progress in Dehydro(genative) Diels–Alder Reaction

“…Wessig and Matthes later reported similarP DDA reactions to afford naphthalenophanes. [43] Upon irradiation( l EXC > 300 nm, pyrex vessel) in tert-butanol, bis-ynones with different linkers smoothly underwent aP DDA reactiont oa fford highly strained 1,5-naphthalenophanes (Scheme 45). This synthetic approach differs from most other routes to naphthalenophanes in that the naphthalene moiety is not presenti nt he reactants.…”

Organische Chemie 2011

“…Eine Photo‐Dehydro‐Diels‐Alder‐Reaktion nutzten Wessig und Matthes, um axial chirale (1,5)‐Naphthalenophane herzustellen 29. Die Idee, 1,3‐Dipole durch Elektronentransfer zu erzeugen, wurde erfolgreich mit sichtbarem Licht und einem RuII‐Katalysator realisiert 30.…”