Intermolecular and Intramolecular Pauson–Khand Reactions of Functionalized Allenes

Low-valent titanium(II) mediated intramolecular and regioselective alkyne/alkoxyallene reductive coupling reactions

Low-valent titanium(II) complexes turned out to be suitable reagents in the promotion of alkyne/alkoxyallene coupling reactions in an intramolecular fashion. The conditions developed herein led to a broad range of highly functionalized cyclic adducts with excellent regioselectivities toward the central carbon of the alkoxyallene moiety. Good yields (up to 76%) were obtained over 19 examples. One-pot late functionalization by electrophile trapping was also possible and led to excellent diastereoselectivities (up to 95/5 d.r.).

PhI(OAc)2-Mediated Regioselective Hydrothiolation of Allenamides with Thiophenol via a Radical Process: Synthesis of Vinyl Sulfides

An efficient PhI(OAc)2-mediated regioselective hydrothiolation of allenamides with thiophenol via a radical process was developed to create a workable route to vinyl sulfides. The reaction exhibits a good functional group tolerance and high efficiency, affording the products in good to excellent yields. Mechanistic investigations indicated that the radical cascade proceeds through an allyl radical intermediate, which is formed via the addition of the PhS radical to the central carbon of allenamides. Moreover, the reaction was also efficient with selenophenol, providing the corresponding product, vinyl selenide, in a 99% yield.

Asymmetric Total Synthesis of Bufospirostenin A

The first and asymmetric total synthesis of bioactive bufospirostenin A, an unusual spirostanol with rearranged A/B rings, was accomplished. The synthetically challenging [5-7-6-5] tetracyclic ring system, found in bufospirostenin A and some other natural products, was efficiently constructed by the unique intramolecular rhodium-catalyzed Pauson-Khand reaction of an alkoxyallene-yne. The 11 stereocenters in the final product, including the 10 contiguous stereocenters, were installed diastereoselectively.

Highly N2-selective allylation of NH-1,2,3-triazoles with allenamides mediated by N-iodosuccinimide

We report a new protocol to synthesize N²-allyl-substituted 1,2,3-triazoles via NIS mediated allylation of allenamides with NH-1,2,3-triazoles.

Regioselective 1,2-addition of allenamides with N-haloimides: synthesis of 2-halo allylic aminal derivatives

A strategy for the synthesis of 2-halo allylic aminal derivatives through regioselective 1,2-addition of allenamides with N-haloimides is presented. This reaction was conducted under very mild conditions and gave up to 99% yield. Moreover, the obtained halides allow functional group diversification by palladium-catalyzed coupling reactions, which could act as potential intermediates for the synthesis of valuable compounds.

NIS-Mediated intermolecular hydroamination of allenamides with imidazole heterocycles: a facile protocol for the synthesis of allylic N,N-acetals

We report a new protocol to synthesize allylic N,N-acetal derivatives through NIS-mediated hydroamination of allenamides with imidazole heterocycles.

Cs2CO3-Catalyzed Synthesis of N-Sulfonyl-Substituted Allenamides

Several novel N-sulfonyl substituted allenamides were obtained in good yields via Cs2CO3-catalyzed isomerization of propargyl amides in THF at room temperature. The easily available starting materials and mild reaction conditions are features of this protocol.

Optimizing ring-opening polymerization of ε-caprolactone by using aluminum complexes bearing amide as catalysts and their application in synthesizing poly-ε-caprolactone with special initiators and other polycycloesters

A series of aluminum complexes bearing amidate ligands, including acylamide, sulfonamide, and aryl carbamate, was synthesized.

A highly efficient tandem [3 + 2] “click” cycloaddition/6-exo-cyclization strategy for the construction of triazole fused pyrazines

The pharmaceutically important tetrahydro-[1,2,3]triazolopyrazine heterocyclic architecture has been synthesized via a concise tandem “click”/6-exo-dig cyclization strategy under mild conditions in mixed aqueous–organic media.

Thermal intramolecular [4 + 2] cycloadditions of allenamides: a stereoselective tandem propargyl amide isomerization-cycloaddition

A stereoselective intramolecular normal demand [4 + 2] cycloaddition of allenamides under thermal conditions without metal assistance is described. This work led to the development of a stereoselective tandem propargyl amide-isomerization-[4 + 2] cycloaddition sequence amenable for rapid assembly of complex nitrogen heterocycles.

Synthesis of amido-spiro[2.2]pentanes via Simmons-Smith cyclopropanation of allenamides

A detailed account of Simmons-Smith cyclopropanations of allenamides en route to amido-spiro[2.2]pentanes is described here. While the diastereoselectivity was low when using unsubstituted allenamides, the reaction is overall efficient and general, representing the most direct synthesis of both chemically and biologically interesting amido-spiro[2.2]pentane systems. With alpha-substituted allenamides, while the diastereoselectivity could be improved significantly based on a series of conformational analyses, both mono- and bis-cyclopropanation products were observed. Consequently, several structurally intriguing amido-methylene cyclopropanes could also be prepared.