Syntheses of 6,7-Benzotropolones by a Sequence of Acylation (or α-Hydroxyalkylation/Oxidation), Ring-Closing Metathesis, and Hydrolysis/ß-Elimination.

Starting from ortho-bromostyrenes, 12 6,7-benzotropolones were synthesized in 3 or 4 steps. Br/Li exchanges provided the respective ortho-lithiostyrenes. The latter were acylated by a Weinreb amide, if unhindered, or hydroxyalkylated by an aldehyde, if hindered (an oxidation ensuing thereafter). Acetonide-containing benzannulated nonatrienones resulted. Ring-closing olefin metatheses converted them into acetonide-containing benzocycloheptadienones. Treatment with aq. HCl caused hydrolyses followed by ß-elimination reactions giving 6,7-benzotropolones.

A Simply Synthesized, Tough Polyarylene with Transient Mechanochromic Response.

A simple and high-yielding route to tough polyarylenes of the type poly(meta,meta,para-phenylene) (PmmpP) is developed. PmmpP is tough even in its as-synthesized state which has an intermediate molar mass of Mw ≈60 kg mol-1 and exhibits outstanding mechanical properties at further optimized molecular weight of Mw =96 kg mol-1 , E=0.9 GPa, ϵ=300 %. Statistical copolymers with para,para-spiropyran (SP) are mechanochromic, and the toughness allows mechanochromism to be investigated. Strained samples instantaneously lose color upon force release. DFT calculations show this phenomenon to be caused by the PmmpP matrix that allows build-up of sufficiently large forces to be transduced to SP, and the relatively unstable corresponding merocyanine (MC) form arising from the aromatic co-monomer. MC units covalently incorporated into PmmpP show a drastically reduced half life time of 3.1 s compared to 4.5 h obtained for SP derivatives with common 6-nitro substitution.