Third-row transition metal catalysts remain a largely untapped resource in cycloaddition reactions for the formation of medium-sized rings. Herein, we report the first examples of iridium-catalyzed inter- and intramolecular vinylcyclopropane (VCP)-alkyne (5+2) cycloadditions. DFT modeling suggests that catalysis by iridium(I) proceeds through a mechanism similar to that previously reported for rhodium(I)-catalyzed VCP-alkyne cycloadditions, but a smaller free energy span for iridium enables substantially faster catalysis under favorable conditions. The system is characterized by up to quantitative yields and is amenable to an array of disubstituted alkynes and vinylcyclopropanes.
Cyclometallated aryl-pyridine gold(iii) complexes are shown to be efficient catalysts for the multicomponent reaction between N-benzyl imines, alkynes, and acyl chlorides to form trisubstituted oxazoles. The reaction typically proceeds in good yields (up to over 80%) and short reaction times (∼15 minutes). The high stability of the investigated cyclometallated catalysts enables a retained efficiency for this reaction in terms of rate and yield using as little as 0.5 mol% catalyst, a reduction by an order of magnitude compared to previously used Au(iii)-salen complexes. An attractive feature of the present catalytic system is that active catalysts can be formed from simple pre-catalysts under the reaction conditions. Both cyclometallated and non-cyclometallated complexes were characterized in the solid state by single crystal X-ray diffraction.
The reaction between N‐benzylpropargylamines and acid chlorides at elevated temperatures provides efficient, direct access to a variety of di‐ and tri‐substituted oxazoles. The versatility of this reaction is explored and 21 examples are demonstrated. The usefulness of the methodology is showcased through the short and efficient formal syntheses of medicinally relevant drugs aleglitazar and romazarit.
A convenient method for the synthesis and isolation of highly reactive formylsilanes by oxidative cleavage of α-silyl glycols is presented. The mild conditions provide an entry to acid- and heat-sensitive members of this theoretically intriguing class of compounds. The utility of the method is demonstrated through the isolation and subsequent diastereoselective derivatization of t-BuMe2- and t-BuPh2-formylsilanes, previously not reported in isolated form.
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