Recent advances in controllable/divergent synthesis

• Jilei Cao,
• Leiyang Bai and
• Xuefeng Jiang

Beilstein J. Org. Chem. 2025, 21, 890–914, doi:10.3762/bjoc.21.73

• ) and (3 + 2) cyclization strategies. Two distinct pathways were established: (1) The titanium-catalyzed ring opening of bicyclobutane (BCB) 32 generates a γ-carbonyl radical intermediate Int-42, which undergoes trapping by vinylazide 33. Subsequent dinitrogen extrusion produces an iminyl radical

(Bio)isosteres of ortho- and meta-substituted benzenes

• H. Erik Diepers and
• Johannes C. L. Walker

Beilstein J. Org. Chem. 2024, 20, 859–890, doi:10.3762/bjoc.20.78

• carbene insertion into bicyclobutane was reported in 2022 by Bychek and Mykhailiuk [74]. Previously the same group had also reported the synthesis of BCPs containing a difluorinated bridge by CF2 carbene insertion into bicyclobutanes [75]. More recently Davies and co-worker reported the one-pot synthesis

• of bridge difluorinated BCPs from α-allyldiazoacetates. In their reaction sequence, intramolecular cyclopropanation first forms the bicyclobutane which is then subjected to CF2 carbene insertion to yield the BCP [76]. Another useful pathway to 1,2,3-BCPs is strain release functionalisation as was

• examples of 1,2,4-trisubstituted BCHs were synthesised by Cairncross and Blanchard in 1966 by strain release [2π + 2σ] cycloaddition of bicyclobutane and alkenes [56]. Intramolecular crossed [2 + 2] cycloaddition frequently employed to access disubstituted BCHs is a useful tool in the synthesis of

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

The cyclopropylcarbinyl route to γ-silyl carbocations

• Xavier Creary

Beilstein J. Org. Chem. 2019, 15, 1769–1780, doi:10.3762/bjoc.15.170

• the γ-trimethylsilyl group. When the substituent is electron-withdrawing (CF3, CN, or CO2CH3), significant amounts of bicyclobutane products are formed. The bicyclobutanes are a result of γ-trimethylsilyl elimination from the cationic intermediate that has an unusually long calculated Si–C bond. The

• solvolysis chemistry of mesylate and triflate derivatives of trans-1-hydroxymethyl-2-trimethylsilylcyclopropane and 1-substituted analogs can be quite different since these substrates do not generally lead to 3-trimethylsilylcyclobutyl cations. Keywords: bicyclobutane; carbocation; cyclopropylcarbinyl

• cation (a cation containing hypercoordinated carbon) that could be derived from protonation of bicyclobutane [20]. Another potential mode of stabilization is by an interaction of the cationic center with the adjacent strained cyclobutyl bonds as in 7b. A second class of carbocations that this article

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225