Synthesis of (+)-Hypoxylactone through Allenoate γ-Addition: Revision of Stereochemistry

Synthesis of (+)-Xylogiblactones B and C through a Kinetic Resolution of the Allenoate γ-Addition: Stereochemical Establishment

Concise syntheses of naturally occurring γ-butenolides (+)-xylogiblactones B and C have been achieved for the first time starting from commercial methyl crotonate in 5-8 steps. The synthetic course involves allenoate γ-addition to racemic aldehydes through a kinetic resolution to establish the required stereochemical framework as center and axial chirality and subsequent oxacyclization via gold catalysis to complete the (+)-xylogiblactone skeleton. Both key transformations proceed in a regio- and stereospecific manner. This outcome relies on finding an efficient synthetic method for racemic aldehydes as precursors for the kinetic resolution. Completion of the synthesis provides stereochemical clarification for (+)-xylogiblactones B and C.

One-Pot Tandem Nickel-Catalyzed α-Vinyl Aldol Reaction and Cycloaddition Approach to [1,2,3]Triazolo[1,5-a]quinolines

A one-pot tandem approach to [1,2,3]triazolo[1,5-a]quinolines was developed from (E)-β-chlorovinyl ketones and 2-azidoaryl carbonyls using a sequence of α-vinyl aldol and azide-alkyne cycloaddition reactions. In particular, the intramolecular azide-alkyne cycloaddition of allenol intermediates was readily promoted by a synergistic action of NEt₃ and nickel catalysts. Given that the [1,2,3]triazolo[1,5-a]quinolines are useful synthetic precursors to α-diazoimines through ring-chain isomerization process, the subsequent denitrogenative transformations should provide ready access to valuable heterocyclic compounds.

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

The allene functionality has participated in one of the most exciting voyages in organic chemistry, from chemical curiosities to a recurring building block in modern organic chemistry. In the last decades, a special kind of allene, namely, allenol, has emerged. Allenols, formed by an allene moiety and a hydroxyl functional group with diverse connectivity, have become common building blocks for the synthesis of a wide range of structures and frequent motif in naturally occurring systems. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This Review summarizes the most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products.