A search for protonated cyclobutane

Abstract

Attempted protonation of cyclobutane with H2SO4-t or CF3COOH-t failed to give any open chain butyl product as evidence for the formation of protonated cyclobutane. The treatment of cyclobutane with an excess of CF3SO3H-t in a sealed tube at 75 °C for 3 days followed by hydrolysis did give rise to the four isomeric butyl alcohols containing some T-label in the butyl groups. The upper limit for this ring cleavage, probably via protonated cyclobutane, was about 1%. H–T exchange in the recovered cyclobutane was also observed.

Triple-Dearomative Photocycloaddition: A Strategy to Construct Caged Molecular Frameworks

“…25 We next explored substrate scope using various chromone substrates 30 − 34 (Table 4), which involved processing of the corresponding crude, caged products using conditions developed in Figure 5. Switching the methyl group of chromone 3 into a hydrogen (30) or a methoxy group (31) did not interfere with the formation of the caged products. Accordingly, endoperoxide 35 was generated in 45% yield from 30 using flow conditions followed by endoperoxidation (Table 4, entry 1).…”

“…Mechanistically, we believe that cyclobutane edge protonation , in the presence of adventitious D-Cl may open the cyclobutane ring of 24 to a transient cation 27 , which is stabilized by the silicon β-effect , followed by elimination and aromatization to afford product 25 (Figure B). Originally, we considered that 25 may be converted back to 24 via dearomative [2 + 2]-cycloaddition as DFT computational analysis (r 2 SCAN-3C/CPCM (CH 2 Cl 2 )) of 25 showed a close distance between the corresponded alkene and the two carbons of the arene (Figure C).…”

Triple-Dearomative Photocycloaddition – A Strategy to Construct Novel Caged Molecular Frameworks

“…Mechanistically, we believe that cyclobutane edge protonation 27,28 in the presence of adventitious D-Cl may open the cyclobutane ring of 25 to a transient cation 28 which is stabilized by the silicon -effect 29,30 followed by elimination and aromatization to afford product 26 (Figure 6B). Originally, we considered that 26 may be converted back to 25 via dearomative [2+2]-cycloaddition as DFT computational analysis (r 2 SCAN-3C/CPCM (CH2Cl2)) of 26 showed a close distance between the corresponded alkene and the two carbons of the arene (Figure 6C).…”

Isotopic exchanges in the treatment of cyclopentane or cyclohexane with some deuterated or tritiated acids

“…The treatment of cyclobutane with I -t , CF,SO,D (2-d), or ['H]CF,SQ3H (2-0 failed to give any significant amount of open chain butyl product. but a facile incorporation of the T-label from 2-t into the hydrocarbon layer was observed ( 5 ) . This exchange was recently shown to involve a carbocationic chain mechanism and quenching with M,O led to the detection of cyclobutanol, cyclopropylcarbinol, and allylcarbinol, indicating the formation of the bicyclobutonium ion (6).…”