Bradsher Cyclization
The Bradsher cyclization, also known as the Bradsher cycloaddition, is a form of the Diels–Alder reaction. It involves the [4+2] addition of a common dienophile to a conjugated diene, resulting in a six-membered ring. This reaction was first reported by C. K. Bradsher and T. W. G. Solomons in 1958[2].
The Bradsher cyclization is an acid-catalyzed reaction used for synthesizing polycyclic aromatic compounds, especially the phenanthrene series[17]. It refers to the acid-catalyzed aromatic cyclodehydration of ortho-acyl diarylmethanes to form anthracenes[19].
There are also modifications of the Bradsher cyclization, such as the hetero-Friedel-Crafts-Bradsher cyclizations, which allow the replacement of ring carbon atoms by heteroatoms, leading to the formation of ring carbon-heteroatom (P, S) bonds[3]. Another modification involves the use of O,S-acetals in the oxo-Friedel-Crafts-Bradsher cyclization[9].
The original Bradsher cyclization reaction requires drastic reaction conditions, such as extremely high temperatures, high concentrations of inorganic acids, and the use of sealed tubes. However, modifications have allowed the use of much milder reaction conditions, such as room temperature and water as a reaction medium[15].
Citations:
[1] https://www.lookchem.com/Chempedia/Basic-Chemical/Chemical-Reaction/8234.html
[2] https://en.wikipedia.org/wiki/Bradsher_cycloaddition
[3] https://pubmed.ncbi.nlm.nih.gov/33114241/
[4] https://www.sciencedirect.com/science/article/pii/S1350417718319096
[5] https://www.youtube.com/watch?v=FuO0YihTD-U
[6] https://www.drugfuture.com/OrganicNameReactions/ONR58.htm
[7] https://en.wikipedia.org/wiki/Diels%E2%80%93Alder_reaction
[8] https://synarchive.com/named-reactions/bradsher-cyclization
[9] https://www.mdpi.com/1420-3049/28/6/2474
[10] https://pubs.acs.org/doi/10.1021/ja01151a069
[11] https://www.mdpi.com/1996-1944/13/21/4751
[12] https://www.sciencedirect.com/science/article/abs/pii/S1350417718319096
[13] https://pubs.rsc.org/en/Content/ArticlePDF/1990/P1/P19900000413
[14] https://link.springer.com/chapter/10.1007/978-3-319-03979-4_38
[15] https://www.cbmm.lodz.pl/pliki/2019/03/Kowalska_streszczenie_ang.pdf
[16] https://chemrxiv.org/engage/api-gateway/chemrxiv/assets/orp/resource/item/6172f639913a741ff6650772/original/efficient-synthesis-and-functionalization-of-3-bromo-naphtho-2-3b-thiophene.pdf
[17] https://www.chemistry-online.com/organic-chemistry/named-reactions/bradsher-cyclization/
[18] https://www.researchgate.net/publication/335298525_Mono-arylalkythio-substituted_Heteroacenes_of_Exceptional_Thermal_and_Photochemical_Stability_via_Thio-Friedel_CraftsBradsher_Cyclization_Reaction
[19] https://link.springer.com/content/pdf/10.1007/978-3-319-03979-4_38.pdf
[20] https://www.lookchem.com/Chempedia/Basic-Chemical/Chemical-Reaction/8230.html
[21] https://www.researchgate.net/figure/Scheme-4-General-mechanism-for-the-oxo-Friedel-Crafts-Bradsher-cyclization-reaction_fig3_369610451