Ring‐Opening/Expansion Rearrangement of Cycloprop[2,3]inden‐1‐ols Catalyzed by p‐Toluenesulfonic Acid

Abstract

A divergent approach to generate either 1-hydroxymethylindenes (which could then be converted to benzofulvenes through a dehydration reaction) or naphthalenes by the rearrangement of cycloprop[2,3]inden-1-ols is reported. The effect of the cyclopropyl ring substitution pattern on ringopening/expansion rearrangements of the substrates was systemically studied.

Synthesis of Bicyclo[2.1.1]hexan‐5‐ones via a Sequential Simmons‐Smith Cyclopropanation and an Acid‐Catalyzed Pinacol Rearrangement of α‐Hydroxy Silyl Enol Ethers

“…Alternatively, 1,2‐rearrangement of bicyclo[3.1.0]hexanes offers a potential pathway for the formation of BCHs, and a semi‐pinacol rearrangement of an alkoxy bicyclo[3.1.0]hexane‐2‐diazonium intermediate has been reported to furnish bicyclo[2.1.1]hexan‐5‐one in a low yield [17] . Although this literature precedent and the known potential side reactions (ring‐expansion to generate cyclic alkenes, [17,18] nucleophilic ring‐openings [18d,19] ) associated with the bicyclo[3.1.0]hexane skeletal framework suggested that this type of molecular rearrangement could be challenging, we believed that the development of a 1,2‐rearrangement process with 2‐substituted bicyclo[3.1.0]hexan‐2‐ols could be an effective synthetic strategy to obtain 1‐substituted bicyclo[2.1.1]hexan‐5‐ones. Herein, we report an acid‐catalyzed pinacol rearrangement reaction to access 1‐substituted bicyclo[2.1.1]hexan‐5‐ones (Scheme 1b, path d) and subsequent functionalization of the ketone moiety to generate disubstituted BCHs that could potentially behave as ortho ‐functionalized benzene bioisosteres.…”

“…However, the resulting bicyclic ring was prone to decomposition during the purification process, and we opted to use the crude material directly for the pinacol rearrangement reaction. Our starting point for the rearrangement step was the reported conditions for the p ‐TsOH‐catalyzed rearrangement of cycloprop[2,3]inden‐1‐ols (entry 1) [18d] . Unfortunately, the desired bicyclic ketone 2 a was not observed under these conditions and the only significant product was the undesired α,β‐unsaturated ketone 3 a .…”

Synthesis of Benzofulvenes via Cp*Co(III)-Catalyzed C–H Activation and Carbocyclization of Aromatic Ketones with Internal Alkynes

“…Purification by column chromatography on silica gel (eluent: petroleum ether) afforded the mixture of 3ah and 3ah′ as a yellow oil (18.3 mg, 42% yield); 1 H NMR (400 MHz, CDCl 3 ): δ 7.65 (d, J = 7.2 Hz, 2.10H), 7.61 (d, J = 6.8 Hz, 1H), 7.47–7.42 (m, 8.68H), 7.36–7.28 (m, 11.84H), 7.24–7.18 (m, 4.85H), 6.09 (s, 3.10H), 5.78 (s, 1H), 5.58 (s, 2.10H), 2.20 (s, 6.30H), 2.18 (s, 3H); 13 C­{ 1 H} NMR (100 MHz, CDCl 3 ): δ 148.6, 147.4, 143.8, 143.5, 141.4, 138.4, 137.1, 136.1, 136.0, 135.0, 134.9, 133.0, 130.3, 129.0, 128.4, 128.2, 128.1, 128.0, 127.4, 126.9, 125.4, 124.9, 119.4, 119.3, 119.1, 118.6, 111.7, 110.6, 11.4, 10.5. The spectral data were in accordance with the literature. , …”