Preparation of Helicenes through Olefin Metathesis

Abstract

Metathesis with a twist! A ring‐closing‐metathesis strategy has been developed for the preparation of various substituted [5]helicene motifs and [6]‐ and [7]helicenes. The two optimized protocols include one method that utilizes the Grubbs second‐generation catalyst under microwave‐irradiation conditions and another that employs a modified Grubbs–Hoveyda catalyst at 40 °C in a sealed reaction vessel. (Mes=mesityl)

Microwave‐Assisted Olefin Metathesis

“…Another particularly challenging example concerns some substituted [5]helicenes and [6]-and [7]helicenes which have been synthesized by olefin RCM through classical thermal heating with the H-G catalyst or, advantageously, under µW irradiation with the G-II catalyst, as illustrated for the [6]helicene 14 (Scheme 7). [24] A highlight of this method is the facile formation of various substituted helicenes from readily available binaphthyls or phenanthryls. This ease of functionalization suggests that the method could be of significant interest in the fields of materials science and medicinal chemistry.…”

A new era for organic synthesis—highlights of the recent progress

“…Collins et al [16] developed a novel approach to the synthesis of helicenes on the basis of RCM, which represent successful examples in this field with bright application prospects. (Scheme 1-3)…”

“…(Scheme [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] On the basis of their previous work on enone radial reaction with amines leading to lactams, Ryu et al [56] designed a new cascade reaction consisting of a terminal alkyne radical triggered carbonylation followed by an addition of amine leading to α-methylene amides (Scheme 1-20). The reaction worked out nicely.…”

Preparation of cyclic molecules bearing “strained” olefins using olefin metathesis

“…This work clearly demonstrates that unstrained benzene rings can be constructed from divinyl precursors using 6 as catalyst. Collins and co-workers subsequently examined whether olefin metathesis could be feasible as a route to the strained benzenes found embedded in the [5] helicene structure [35]. Although strained, the normally competing reverse ringopening reaction would not be possible.…”