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We examine the effects of fusing two benzofurans to s‐indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3‐functionalized benzofuran yields syn‐IDBF and syn‐IIDBF. syn‐IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn‐IIDBF. In the case of the anti‐isomers, synthesized via 2‐substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring‐opening reaction during the final dearomatization step. All the results are compared to the benzothiophene‐fused analogues and show that the increased electronegativity of oxygen in the syn‐fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. For syn‐IIDBF increased diradical character results from rearomati‐zation of the core naphthalene unit in order to relieve this paratropicity. [ABSTRACT FROM AUTHOR]

The serendipitous isolation of very small amounts of two naphthocyclobutadiene (NCB) derivatives has led to the computational re‐examination of the electrocyclization of Z,Z‐3,5‐octadiene‐1,7‐diyne as well as the experimental and computational study of diethynylindeno[2,1‐a]fluorene derivatives that contain the 3,5‐octadiene‐1,7‐diyne motif as part of a larger π‐framework. In both cases the calculated potential energy surface strongly implicates two successive electrocyclic reactions to afford the antiaromatic products. With the octadienediyne fragment locked in the reactive conformation, the postulated diethynylindeno[2,1‐a]fluorene intermediates afford the NCBs in modest to good yields. X‐ray crystallography of four NCBs as well as NICS‐XY scan calculations show that the paratropic motif is located primarily in the benzocyclobutadiene fragment within the larger π‐scaffold. [ABSTRACT FROM AUTHOR]