Anhydrides of Arylfuran and Arylpyran Pseudoacids: Formation and Structures; C–O Bond Lengths Trends in Pseudo o-Formylbenzoic Acid Derivatives
Three methods for producing anhydrides of arylfuran and arylpyran pseudoacids were explored. These included thermal dehydration, phosgene or thionly chloride activation and decomposition, and dicyclohexylcarbodiimide activation and coupling. Derivatives of the cyclic forms of o-formylbenzoic acid, o-acetylbenzoic acid, 2-carboxyphenylacetaldehyde and of 4,4-dimethyl-3,4-dihydro-3-hydroxy-[1H]-isobenzopyran-1-one were formed including dipseudoanhydides and normal-pseudo anhydrides. Crystal and molecular structures for meso and (R,R/S,S)-bis(1[3H]-isobenzofuranone-3-yl)ether, (R,R/S,S)-bis(3-methyl-1[3H]-isobenzofuranone-3yl)ether, meso (3,4-dihydro-[1H]-isobenzopyran-1-one-3-yl)ether, 3-benzoyloxy-1[3H]-isobenzofuranone, 3-benzoyloxy-3-methyl-1[3H]isobenzofuranone, 3-(4′-nitrobenzoyloxy)-4,4-dimethyl-3,4-dihydro-[1H]-isobenzopyran-1-one, and (1[3H]-isobenzofuranone-3-yl)(4,4,dimethyl-3,4-dihydro-[1H]-isobenzopyran-1-one-3-yl)ether are reported. Endocyclic pseudoacyl C–O bonds are always longer than the exocyclic pseudoacyl C–O bonds. It is possible to refine the previously established C–O bond length dependencies on the pKa (of the conjugate acids) of the leaving groups for 3-substituted 1-[3H]-isobenzofuranones. Of six dipseudoanhydrides studied, conformations are found with exocyclic C–O(ether) linkages synclinal to the endocyclic C–O and away from the ring (exo conformation) in two meso structures, two of three RR/SS forms and in a chiral unsymmetrical form. An endo conformation is observed in one of the RR/SS forms. In three normal-pseudo anhydrides, both endo and exo conformations are observed.
KeywordsPseudoacids Anhydrides Coupling reactions C–O bonds Bürgi-Dunitz angle
We thank Marilyn Brooks, Brian MacFarland, Derek Thomas Letort for early synthetic explorations. EJV thanks the National Science Foundation for support of crystallographic equipment (MRI-0604188).
- 5.Wolf L (1885) Zur Kenntniss der Terpene und der ätherischen Oele. Annalen 229:258Google Scholar
- 9.Lalancette RA, Vanderhof PA, Thompson MW (1990) 2-Benzoylbenzoic acid: structures and hydrogen-bonding patterns of the anhydrous and hydrated form. Acta Crystallogr A C46:1682–1686Google Scholar
- 19.Letort DT (2000) Synthetic methods towards pseudoacid derivatives. Honors Essay, Mississippi College, ClintonGoogle Scholar