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Thermolysis of pentasubstituted 3‐hydroxy‐1,2‐dioxolanes
Author(s) -
Baumstark A. L.,
Vasquez Pedro C.
Publication year - 1992
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570290718
Subject(s) - chemistry , homolysis , diradical , thermal decomposition , medicinal chemistry , bond cleavage , fragmentation (computing) , radical , photochemistry , decomposition , benzene , organic chemistry , catalysis , operating system , computer science , physics , nuclear physics , singlet state , excited state
A series of pentasubstituted 3‐hydroxy‐1,2‐dioxolanes, la‐e , was synthesized by oxygen trapping of β‐keto radicals formed during α‐azo hydroperoxide decomposition. Thermolysis of the pentasubstituted 3‐hydroxy‐1,2‐dioxolanes (hemiperketals) in benzene proceeded cleanly and yielded pairs of ketones and carboxylic acids. Two of the hemiperketals yielded only one pair of products while the others produced two sets of products. One of each pair of fragmentation products had undergone skeletal rearrangement. Only methyl migrations were observed when in competition with phenyl groups from the same position. The activation parameter data for ld [ΔH‡ = 24.3 kcal/mol, ΔS‡ = ‐8.4 eu, ΔG‡ = 27.1 kcal/mol, k 60° . = 3.1 × 10 −5 s −1 ] were consistent with 0.0 bond scission as the rate‐determining‐step. A likely mechanism for this thermolysis is initial peroxy bond homolysis to the 1,5‐oxygen diradical followed by β‐scissions with rearrangements.