Since the first secondary and tertiary alkoxycarbonium ions were prepared by Maerwein, et 1 al , further isolation, observation, and spectral studies of tertiary, secondary 2-6 and primary' examples have been reported including dioxolenium cations 396 .
Alkoxycarbonium ions possess large gaseous stabilization energies compared to the methyl cation8".
The stabilization energy of CH30CH2+ is 68 kcal compared to 35 kcal for CH3CH2+8.
Stable trialkylthiomethyl cations have also been reported 10-12 .
We report the cyclization of ally1 and methallyl esters and thiol esters to cyclic dioxolenium and oxthiolenium cations in strong proton acids.
In 96, 80, and 60% H2S04 and FS03H,
No.5
We suggest that CH3COOH2' is generated by ring opening to the methallyl (or allyl) derivatives followed by AAL-is fission.
Attempts to cyclize several acetates and benzoates of secondary allylic alcohols* in 96% H2S04 in esch case led to immediate quantitative cleavage. AAL-fission of these esters would generate CIi3COOH2+ and secondary allylic carbonium ions which are unstable in 96% H2S04 and cascade to complex mixture of cyclopentenyl cations.** * Included in this series were J-scetoxy-pentene-1, 3-benzoyloxypentene-1, 3-acetoxy-2methylpentene-1, and 2-scetoxy-2-methyl-2-pentene.
*Cyclopentenyl cations sre rapidly generated from mono, di, and trisubstituted. allylic carbonium ions in 962 H2S04 (ref. 17, 18). The characteristic nmr pattern of a mixture of cyclopentenyl cations was observed in 962 H2S04 after cleavage of ions I, II, IV and the esters in the footnote above.