Gold-catalyzed intermolecular oxidations of internal alkynes have been achieved with high regioselectivities using 8-alkylqinoline N-oxides as oxidants and in the absence of acid additives. Synthetically versatile α,β-unsaturated carbonyls are obtained in good to excellent yields and with excellent E-selectivities. A range of functional groups such as THP, MOMO, N 3 , OTBS, and NBoc are tolerated. This reaction allows to mask α,β-unsaturated carbonyls as propargyl moieties, thus offering a practical solution to issues of functional group compatibility with α,β-unsaturated carbonyls, likely encountered in syntheses of complex structures.Although alkene epoxidation is a classic and versatile reaction in organic synthesis, epoxidation of C-C triple bonds1 with DMDO or peracids has little synthetic utility except with electronically biased ynamide substrates2 as often multiple products including α,β-unsaturated ketones were formed with little chemoselectivity and regioselectivity. Many of the product formations could be rationalized via an initial rearrangement of oxirene A3 into highly reactive α-oxocarbene B (Scheme 1A). In the cases of alternative metal-mediated/ catalyzed intermolecular alkynes oxidation, further oxidation is unavoidable,4 leading to α,β-epoxy ketones,5 1,2-dicarbonyl, or carboxylic products;6 hence, regioselectivity has not been studied nor achieved. Herein, we report a rare highly regioselective single oxidation of internal alkynes via gold catalysis under exceedingly mild conditions, and synthetically versatile α,β-unsaturated carbonyls are directly formed from propargyl moieties for the first time in good yields and with high to excellent regioselectivities.We have recently reported that terminal alkynes or alkynoates can be oxidized intermolecularly into α-oxo gold carbene C,7 which could be trapped efficiently by tethered OH groups.8 We envisioned such a gold carbene intermediate, if generated from internal alkynes, might undergo facile 1,2-C-H insertions, thus avoiding further oxidation and forming highly valuable α,β-unsaturated carbonyls (Scheme 1B). This gold catalysis would make a propargyl moiety a masked α,β-unsaturated carbonyl;9 however, the challenge is how to achieve high regioselectivities10 without much structural bias in the substrate.To our delight, the oxidation of symmetric 6-dodecyne indeed afforded α,β-unsaturated ketone 2a in 77% yield albeit sluggish reaction (Eq. 1). In contrast to cis-C-C double bonds formed in zhang@chem.ucsb.edu. Supporting Information Available: Experimental procedures, compound characterization data. This material is available free of charge via the Internet at http://pubs.acs.org. Rh-catalyzed decomposition of α-diazo carbonyl compounds,11 only trans-2a was observed, reflecting a unique aspect of gold carbene reactivities. NIH Public AccessWith this encouraging result, we then chose non-symmetric aliphatic alkyne 1b to study regioselectivity by tuning the steric and electronic properties of gold catalysts and N-oxides. Table 1 shows some...

The first efficient intermolecular reaction of gold carbene intermediates generated via gold-catalyzed alkyne oxidation has been realized using nitriles as both the reacting partner and the reaction solvent, offering a generally efficient synthesis of 2,5-disubstituted oxazoles with broad substrate scope. The overall reaction is a [2 + 2 + 1] annulation of a terminal alkyne, a nitrile, and an oxygen atom from an oxidant. The reaction conditions are exceptionally mild, and a range of functional groups are easily tolerated. With complex and/or expensive nitriles, only 3 equiv could be sufficient to achieve serviceable yields in the absence of any solvent and using only 1 mol % BrettPhosAuNTf(2) as the catalyst.

Transposable elements (TE) usually take up a substantial portion of eukaryotic genome. Activities of TEs can cause genome instability or gene mutations that are harmful or even disastrous to the host. TEs also contribute to gene and genome evolution at many aspects. Part of miRNA genes in mammals have been found to derive from transposons while convincing evidences are absent for plants. We found that a considerable number of previously annotated plant miRNAs are identical or homologous to transposons (TE-MIR), which include a small number of bona fide miRNA genes that conform to generally accepted plant miRNA annotation rules, and hairpin derived siRNAs likely to be pre-evolved miRNAs. Analysis of these TE-MIRs indicate that transitions from the medium to high copy TEs into miRNA genes may undergo steps such as inverted repeat formation, sequence speciation and adaptation to miRNA biogenesis. We also identified initial target genes of the TE-MIRs, which contain homologous sequences in their CDS as consequence of cognate TE insertions. About one-third of the initial target mRNAs are supported by publicly available degradome sequencing data for TE-MIR sRNA induced cleavages. Targets of the TE-MIRs are biased to non-TE related genes indicating their penchant to acquire cellular functions during evolution. Interestingly, most of these TE insertions span boundaries between coding and non-coding sequences indicating their incorporation into CDS through alteration of splicing or translation start or stop signals. Taken together, our findings suggest that TEs in gene rich regions can form foldbacks in non-coding part of transcripts that may eventually evolve into miRNA genes or be integrated into protein coding sequences to form potential targets in a “temperate” manner. Thus, transposons may supply as resources for the evolution of miRNA-target interactions in plants.

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Direct reductive amination of a wide range of ketones has been accomplished by the cooperative catalysis of an Ir(III)-diamine complex and a chiral phosphoric acid or its conjugate base.