Furan-based helicenes 2c and 2d were obtained in lower yields of 74% and 48%, respectively, compared to the corresponding thieno [4]helicenes. These lower yields may be explained by the formation of singlet oxygen in our Mallory reaction conditions (in the presence of air), which has been reported to undergo selective [4+2] cycloadditions with furans. Thieno [6]helicene 2e and thieno [5]helicene 2f were obtained in 71% and 56% yields respectively. The assembly of the larger thieno [7]helicene 2g in a single step was achieved through a double-Mallory reaction in 73% yield. Notably, the hetero-stilbene precursor 1g is far less soluble in toluene than the shorter hetero-stilbenes, requiring the reaction mixture to be diluted to 0.5 mM. In our hands, azahelicenes were more difficult to synthesise under photochemical conditions than thiahelicenes. We attributed this difference in part to the generation of insoluble ammonium salts upon reaction with the in-situ formed hydrogen iodide before its quenching by THF. These solubility issues were avoided through the use of a 1:1 toluene:MeCN mixture, affording chloro-substituted pyrido [4]helicene 2h in 58% yield. For other substrates, the formation of hydrogen iodide was minimised by using catalytic amounts of iodine and a large excess of the hydrogen iodide scavenger THF (Table ). Under these conditions, the cyclisation of thiazole-containing stilbene 1i led to a 61% yield of ring-closure products; however, the desired thiazolo [4]helicene 2i was only obtained in a 35% yield; comparable to that of a literature reported thiazole-based helicene. The remaining mass balance of ring-closure products was the side product 2i', obtained in 26% yield after the opening of the thiazole ring in the product 2i. No comparable ring-opening was observed for oxazolo [5]helicene 2k, which was synthesised in a 40% yield. While the Mallory reaction is mostly regioselective, chloro-substituted pyridohelicenes 2m and 2m' were afforded in a 7:3 ratio (51% and 19% yield) in favour of the more sterically hindered product 2m. Similarly, thiadiazolo [5]helicene 2n was obtained in 54% yield alongside 17% of the linear side product 2n', improving on the literature precedent where the ratio of desired helicene to linear product was 1:1. 61 In the case of quinolinyl substrate 1o, it was found that the use of the 150 W UV lamp was unsuitable. Preliminary test reactions showed very low NMR yields of our desired product, but upon switching to a 60 W UV lamp our NMR yields of product 2o improved to 44%. We propose that a weaker lamp may reduce the conversion of desired product 2o into the doubly cyclised perylene-like structure 2o', which has been reported to be a typical side product of [5]helicene synthesis via a Mallory photocyclisation. The cyclisation of the benzothiophene stilbene 1p afforded thieno [7]helicene 2p in 53% yield alongside the S-shaped product 2p' in 18% yield (see SI). The double cyclisation of carbazole-based 1q afforded 788 mg of the dibromo pyrrolo [7]helicene 2q in 71% yield on a 1.2 mmol scale.