Systematic Synthesis of Diphenyl‐Substituted Carotenoids as Molecular Wires

Abstract

A general method for the construction of diphenyl‐substituted carotenoids has been developed through the stereoselective synthesis of dienyl sulfones with a phenyl substituent. Systematic synthetic pathways to the dienyl sulfones were delineated starting from readily available acetophenones with para‐substituent X of various electronic natures, which provided the carotenoids with diverse physicochemical characteristics. The sulfone olefination method together with the Ramberg–Bäcklund reaction produced a 9,9′‐cis‐10,10′‐diphenylcarotene and all‐trans‐9,9′‐diphenylcarotenes. Conductance measurements of the all‐trans carotenoids by the scanning tunnelling microscopy break‐junction method revealed a positional effect of the phenyl groups as well as a polar effect of the phenyl substituent X according to the electronic nature.

Role of Ring Ortho Substituents on the Configuration of Carotenoid Polyene Chains

“…A new E/Z ratio was established in the allyl indium species according to the alkenyl substituents regardless of the original E/Z ratio of allyl halide 8. 24 The oxonia-Cope rearrangement of homoallylic alcohol 10a (R = Ph) was performed using stoichiometric camphoresulfonic acid and aldehyde 9 at 80 °C to provide dienyl sulfone 2a in 77% yield (E/Z = 2:1 at C-2). 22 Milder condition of catalytic Sn(OTf) 2 and aldehyde 9 at 40 °C was utilized for the rearrangement of homoallylic alcohol 10b (R = BT) to give dienyl sulfone 2b in 61% yield (E/Z = 1.5:1 at C-2).…”

“…22 Milder condition of catalytic Sn(OTf) 2 and aldehyde 9 at 40 °C was utilized for the rearrangement of homoallylic alcohol 10b (R = BT) to give dienyl sulfone 2b in 61% yield (E/Z = 1.5:1 at C-2). 24 All-Edienyl sulfone 2a and 2b can be easily obtained by recrystallization from MeOH or EtOH.…”

“…Chlorohydrin formation (58% yield) by NCS in water/DMF followed by bromination (92% yield) with PBr 3 and catalytic CuI accompanying allylic migration produced allylic dihalide 7 ( E : Z = 6:1) . Selective allylation at the more reactive carbon containing bromide by NaSO 2 Ph provided chloroallylic benzenesulfone 8a (60% yield) or by BT-SH using K 2 CO 3 in acetone produced the corresponding BT-sulfide (95% yield). Sulfur oxidation by H 2 O 2 with catalytic sodium tungstate (Na 2 WO 4 ·2H 2 O) gave rise to chloroallylic benzothiazolesulfone 8b (51% yield) .…”

“…Activation of the allylic chloride by Finkelstein reaction (NaI, acetone) was necessary to produce the corresponding homoallylic alcohol 10b (R = BT) in 45% yield with 2:1 antiselectivity. A new E / Z ratio was established in the allyl indium species according to the alkenyl substituents regardless of the original E / Z ratio of allyl halide 8 …”

Synthetic Access to Aromatic α-Haloketones

“…In 2017, Lim and co-workers reported a direct bromination and chlorination route optimised for aromatic ketones [ 66 ]. The procedure involved the addition of NBS (1.05 equiv.)…”