Search

A practical synthesis of benzisoxazole and its conversion to alpha-aryloxyisobutyric acid using 1,1,1-trichloro-2-methyl-2-propanol is developed. A highly reactive, short-lived intermediate derived from chloretone is detected by ReacIR and its half-life determined to be ~5 min.

A variety of indenones and substituted butenolides can be synthesized using the rhodium(II)-catalyzed reaction of type II alpha-diazo carbonyl compounds. Data show that the tandem cyclization-rearrangement exhibits high chemoselectivity facilitating transformations along the synthetic pathway.

The rhodium(II)-catalyzed reaction of diazoamido ester was analyzed to determine the origin of cyclo-addition push-pull stabilized ylides during intramolecular cycloadditions. The formation of tetracycles during the rhodium-catalyzed formation of carbonyl intermediates from cyclic diazo amides was dependent on the presence of the carbonyl group in the tether that was engaged in ring formation. The presence of a carbonyl group in the dipolarophile tether also relieved steric congestion. Furthermore, severe cross-ring 1,3-diaxial crossing promoted a twist-boat conformation.

The apparent 6-endo-dig addition when several (phenylethynyl)aryl-substituted alcohols and ketones with neighboring oxygen atom that readily add to the unactivated triple bond undergo base-induced cyclization is actually a rearrangement of the initial benzofuran derivative. A novel acid-catalyzed rearrangement causes the 5-exo-dig produced to changes to a 6-endo-dig product. of the initially formed benzofuran derivative supported the apparent 6-endo-dig addition. The o-formyl- and o-carbomethoxy-substituted alkynyl alcohols prefer the 6-endo-dig pathway.

Synthesis of benzo-substituted cyclopentenones involves an intramolecular tandem ylide-cycloaddition sequence, catalyzed by Rh(II) carboxylates. The method uses O-alkynyl-substituted alpha-diazoacetophenones having tethered heteroatoms as starting materials, and substituents on the alkyne side chain influence the tandem annulation reaction. X-ray crystallography helps determine the structure of the rearranged cycloadduct. Mechanistic study suggests that ring-opening of a transient intermediate oxabicyclo(2.2. 1)heptane precedes a Wagner-Meerwein rearrangement.