Studies towards iodine-catalyzed dehydrative-cycloisomerization of pent-4-yne-1,2-diols to di- and tri-substituted furans

Recent Advances in the Synthesis of Propargyl Derivatives, and Their Application as Synthetic Intermediates and Building Blocks

The propargyl group is a highly versatile moiety whose introduction into small-molecule building blocks opens up new synthetic pathways for further elaboration. The last decade has witnessed remarkable progress in both the synthesis of propargylation agents and their application in the synthesis and functionalization of more elaborate/complex building blocks and intermediates. The goal of this review is to highlight these exciting advances and to underscore their impact.

Ready Access to Densely Substituted Furans Using Tsuji-Wacker-Type Cyclization

A competent method for the construction of highly substituted furans catalyzed by Pd(II) and Cu(II) chloride has been developed. The method provides easy access to di-, tri-, and tetrasubstituted furans from corresponding diols with relatively mild conditions in a unified strategy. The developed method has been successfully tested with more than 25 substrates, which resulted in furans of multiple substitution patterns with up to 84% isolated yields.

Synthesis of 2-Aryl Acetophenones via Hydrobromination and Oxy-isomerization of (o-Arylethynyl)benzyl Alcohols

Hydrobromination and oxy-isomerization of (o-arylethynyl)benzyl alcohols to yield brominated aryl ketones were achieved with bromotrimethylsilane. The substrate scope suggested that vinyl carbocations, stabilized by the conjugated aryl groups, are the reaction intermediates. 1H-Isochromene was also detected by ¹H NMR, and an isolated 1H-isochromene was converted to the product when retreated with TMSBr. The formation of 1H-isochromene is equivalent to a 6-endo-dig cyclization and contrasts with the corresponding reactions under basic conditions, in which the 5-exo-dig process dominated.

Oxidative C–H Acyloxylation of Acetone with Carboxylic Acids under Iodine Catalysis

Iodine-catalyzed oxidative C(sp3)–H acyloxylation of acetone with carboxylic acids has been developed. The method employs iodide­ as catalyst and sodium chlorite as oxidant. Substituted benzoic acids, naphthoic acids and heteroaromatic carboxylic acids can be used, and 2-oxopropyl carboxylates are obtained with good to excellent yields.

Studies in the rearrangement reactions involving camphorquinone

Skeletal rearrangements of camphor are well-known, however, those involving camphorquinone, its sibling, are rare. We have found that the diol derived from allylated camphorquinone undergoes iodine or bromine mediated deep-seated skeletal rearrangement to provide an interesting tricyclic ring system. The iodo group in the rearranged product provided convenient leverage for further functionalization. For example, it was converted into an azide and the azide was subjected to copper(i) mediated Huisgen 1,3-dipolar cycloaddition with acetylenes to obtain a terpene–triazole conjugate.

We described an unprecedented skeletal rearrangement of camphorquinone motif to an interesting tricyclic ring system.Peripheral functional group modification provided a terpene-triazole conjugate.