Molecular saddles, 3. Hydroxymethyl-functionalised 9,10- bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene pi-electron donors as synthetic intermediates for supramolecular structures

Abstract

The synthesis of new derivatives of 9,10-bis(1,3-dithiol-2- ylidene)-9,10-dihydroanthracene is reported. H-1 NMR studies on compound 4 are consistent with two conformers of the saddle- shaped molecule which interconvert by a boat-boat flipping of the central ring at high temperature. The hydroxymethyl substituent of 4 is readily esterified to yield the benzoyl and 2-naphthaloyl ester derivatives 5a and 5b, respectively, and the dimer and the trimer structures 6 and 7, respectively, by reaction with benzoyl chloride, 2-naphthaloyl chloride, 1,4- benzenedicarbonyl chloride and 1,3,5-benzenetricarbonyl chloride. Deprotonation of 9-(4,5-dimethyl-1,3-dithiol-2- ylidene)-10-(1,3-dithiol-2-ylidene)-9, 10-dihydroanthracene (8) using lithium bis(trimethylsilyl) amide (LHMDS) followed by in situ quenching of the Lithiated intermediate with methylchloroformate gave the diester derivative 10 (96% yield), whereas using LDA gave the monoester 9 as the major product (32% yield). Diester 10 was reduced to the di(hydroxymethyl) derivative 11. The solution electrochemistry of these new compounds has been studied by cyclic voltammetry: the ester substituents of 9 and 10 are conjugated to the pi -framework, causing a positive shift of E-OX. The X-ray crystal structures of compounds 4, 5a, 5b . CH2Cl2, 10 and 11 are reported. The molecules adopt a saddle-like conformation; the bis(1,3- dithiol-2-ylidene)-9,10-dihydroanthracene system is U-shaped due to the boat conformation of the central quinodimethane ring and folding of both the 1,3-dithiole rings. Each compound displays a dimeric packing motif which is most pronounced for 5a and 5b . CH2Cl2. Both these structures contain "oligomeric" acceptor donor stacks: 4-layer ADDA in 5a and 6-layer DADDAD in 5b (D = dithiole; A = benzoyl and naphthoyl, respectively) but neither contains infinite stacks