Expeditious synthesis of helicenes using an improved protocol of photocyclodehydrogenation of stilbenes

Abstract

An improved procedure has been developed for photodehydrocyclization of stilbenes for the synthesis of phenanthrenes and helicenes. This procedure involves the use of THF as a scavenger of hydriodic acid produced during iodine mediated photodehydrocyclization. The use of THF is advantageous due to its higher boiling point, lower cost and easy availability as compared to propylene oxide. The method is applied to synthesize a number of phenanthrenes and helicenes.

Chiral Recognition of Hexahelicene on a Surface via the Forming of Asymmetric Heterochiral Trimers

“…The denominators P and M represent right and left handedness [12], which respectively correspond to the clockwise and anticlockwise descending sequence of the molecular apparent height. The explored [6]H molecules were synthetized by following the reported procedure [23]. A CO functionalized tip was used for the nc-AFM measurements to achieve submolecular resolution [24,25].…”

“…The [6]H molecules were synthesized following the reported procedure of photocyclodehydrogenation of stilbenes [23]. Enantiopure P -[6]H was achieved by a commercial enantioseparation process, followed by absolute configuration determination using electronic circular dichroism (CD) measurement.…”

Continuous flow photocyclization of stilbenes – scalable synthesis of functionalized phenanthrenes and helicenes

“…Optimization of the reaction conditions in a small flow setup (5 mL FEP tubing, 150 W UV-lamp) is presented in Table 1. Although both THF and propylene oxide showed good ability to quench HI, we choose THF as additive due to its lower cost, volatility and toxicity [23–24]. Under the optimized conditions, E -stilbene ( 1a ) could be converted to phenanthrene ( 2a ) in 95% NMR yield with a retention time of 83 min (Table 1, entry 5).…”

Enantioselective Synthesis of 1‐Aryl Benzo[5]helicenes Using BINOL‐Derived Cationic Phosphonites as Ancillary Ligands

“…Once this initial set of gold precatalysts was prepared, their performance on the cyclization of model alkyne 2 a into benzo[5]helicene 1 a was evaluated. This substrate, as with all of general formula 2 , were readily obtained in only two steps via oxidative photocyclization of conveniently substituted stilbenes, followed by Suzuki coupling to install the pending diphenylethyne unit [17] . For details, see the Supporting Information.…”