Dehydrative Alkylation of Phenols with Alcohols via Formation of Triflate.

An efficient synergistic trityl cation ([Ph3C][B(C6F5)4])/triflic anhydride (Tf2O) catalyzed alkylation of phenols with alcohols is reported. Benefiting from the formation of the triflate in situ, cheap and readily available active alcohols can be used as the alkylating reagents, and the reaction proceeds under mild reaction conditions with a broad substrate scope. This protocol enables the synthesis of ortho-selective phenols and 2,4,6-trisubstitued phenols containing three different alkyl groups. tert-Amyl triflate was synthesized, and mechanistic studies support a triflate-mediated alkylation process.

Mechanochemical Solvent-Free Catalytic C-H Methylation.

The mechanochemical, solvent-free, highly regioselective, rhodium-catalyzed C-H methylation of (hetero)arenes is reported. The reaction shows excellent functional-group compatibility and is demonstrated to work for the late-stage C-H methylation of biologically active compounds. The method requires no external heating and benefits from considerably shorter reaction times than previous solution-based C-H methylation protocols. Additionally, the mechanochemical approach is shown to enable the efficient synthesis of organometallic complexes that are difficult to generate conventionally.

Carbocation catalysed ring closing aldehyde-olefin metathesis.

A highly efficient aldehyde-olefin metathesis catalysed by the carbocation, 4-phenylphenyl-diphenylmethylium ion, has been developed. This protocol is characterized by high yields, low catalyst loading (down to 2 mol%), good functional group compatibility and mild reaction conditions.

Cadmium iodide-mediated allenylation of terminal alkynes with ketones.

Allenes are important building blocks in organic synthesis and have attracted much attention from researchers worldwide. So far, mono- and 1,3-disubstituted allenes can be prepared easily by applying the allenylation of terminal alkynes reaction of aldehydes. However, trisubstituted allenes have never been reported using this reaction due to the extremely low reactivity of ketones. Here, we report the one-pot synthesis of trisubstituted allenes from terminal alkynes and ketones utilizing cadmium iodide as the mediator. With this protocol, a series of different allenes, including 1,5-bisallenes and optically active allenols, which are especially important in synthetic chemistry, have been successfully prepared.

Unexpected regioselectivity switch: organophosphine-triggered reactions of cyclopropene-1,1-dicarboxylates with aldehydes.

With tris(4-methoxyphenyl)phosphine as the nucleophilic reagent, the readily available cyclopropene-1,1-dicarboxylates undergo a ring-opening reaction to generate a Wittig-type intermediate, which would react with aromatic aldehydes to yield (E)-5-aryl-2-(methoxycarbonyl)-2,4-pentadienoates. It is interesting to observe that the regioselectivity of the ring-opening reaction is switched.

Bimetallic enantioselective approach to axially chiral allenes.

An efficient bimetallic Zn(II)/Cu(I)-mediated asymmetric synthesis of simple axially chiral allenes from terminal alkynes and aldehydes was realized by taking advantage of the chiral amine (S)-α,α-diphenylprolinol 3. This one-pot procedure is compatible with broad scopes of both terminal alkynes and aldehydes, providing axially chiral allenes in practical yields with an excellent enantioselectivity. Control experiments revealed that CuBr is responsible for the efficient formation of propargylic amine while the combination of CuBr and ZnBr2 plays crucial roles in the amine-to-allene transformation.