Unusual methylation reaction of gem-bromofluorospiropentanes with methyllithium

Cationic Carbenoid Rearrangement of 2‐Phenyl Substituted gem‐Dihalogenospiropentanes

“…gem ‐Dihalogenospiropentanes 1 – 9 were studied in the reaction with methyllithium under appropriate conditions depending on the halogen atoms. Previously, we showed that the most favorable conditions for the rearrangement of gem ‐dibromospiropentanes were –55 °C,2,3 whereas bromofluorospiropentanes reacted with methyllithium at 0 °C or higher temperatures 5. Bromochloro‐substituted spiropentanes 2 , 5 , and 8 were treated with methyllithium at –65 °C.…”

“…However, we have recently reported that some gem ‐dihalogenospiropentanes react with methyllithium in an unusual way: lowering the reaction temperature prevents the formation of allenes and leads to carbenoid skeletal rearrangement 2. The final steps of this reaction are quite variable and may include halogenophilic processes,3 insertion into a C–H bond of the solvent,4 and substitution of the halogen atom for a methyl group 5. The preferable reaction path is determined by the substituents in the spiropentane moiety as well as by the nature of the halogen atoms (Scheme ).…”

Recent advances in the syntheses, transformations and applications of 1,1-dihalocyclopropanes

“…29 The bromofluorocyclopropane derivative of bromo-47a or methoxybenzonorbornadiene 47b was obtained in low yields by the addition of bromofluorocarbene generated from dibromofluoromethane in the presence of NaOH and a suitable phase transfer catalyst (Scheme 19). 29 The bromofluorocyclopropane derivative of bromo-47a or methoxybenzonorbornadiene 47b was obtained in low yields by the addition of bromofluorocarbene generated from dibromofluoromethane in the presence of NaOH and a suitable phase transfer catalyst (Scheme 19).…”

Recent developments in the reactivity of methylene- and alkylidenecyclopropane derivatives

“…In 2009, these authors also reported the synthesis of a series of novel bromofluorospiropentanes in moderate-to-good yields (35e92%) by the [1þ2] cycloaddition of bromofluorocarbene, in situ generated from CHBr 2 F, to the corresponding methylenecyclopropanes in the presence of 50% NaOH and TEBAC. 120 121 The reaction was performed in the presence of Ni(cod) 2 combined with tri-o-biphenylyl phosphate as ligand. With symmetrical 2,3-disubstituted 1,3-butadienes, the corresponding cycloheptenes were formed as single products in 38e70% yields, whereas the reaction of 2-substituted 1,3-butadienes led to the formation of the corresponding cycloheptenes as mixtures of two regioisomers in 0e68% yields, according to the nature of the substituents.…”