Oxamidation of Unsaturated O-Alkyl Hydroxamates: Synthesis of the Madangamine Diazatricylic (ABC Rings) Skeleton

An Environmentally Benign Multicomponent Cascade Reaction of 3-Formylchromones, 2-Naphthols, and Heterocyclic Ketal Aminals: Site-Selective Synthesis of Functionalized Morphan Derivatives

A novel protocol has been developed for the preparation of highly functionalized 2-azabicyclo[3.3.1]nonane (morphan) derivatives by the interesting three-component cascade reaction of 3-formylchromones, 2-naphthol, and heterocyclic ketal aminals (HKAs) in the ionic liquid [BMIM]PF₆ promoted by the organic base Et₃N. A complex cascade reaction is required, which includes a 1,2-addition, two Michael reactions, two tautomerizations, and an N-alkylation accompanied by a ring-opening reaction and involving the cleavage of one C-O bond and the formation of four bonds (one C-N bond, one C-O bond, and two C-C bonds). As a result, functionalized morphans (5 and 6) bearing naphthalene-structured skeletons were prepared by simple heating of a mixture of 3-formylchromones, 2-naphthols, and HKAs in the environmentally friendly ionic liquid [BMIM]PF₆. This protocol can be used in the synthesis of various morphans and is suitable for combinatorial and parallel syntheses of natural-like morphan derivatives. This approach has several advantages such as the use of an environmentally friendly solvent, simple and practical operation (multicomponent one-pot reaction), and satisfactory yields (65-88%).

A New Organocatalytic Desymmetrization Reaction Enables the Enantioselective Total Synthesis of Madangamine E

The enantioselective total synthesis of madangamine E has been completed in 30 steps, enabled by a new catalytic and highly enantioselective desymmetrizing intramolecular Michael addition reaction of a prochiral ketone to a tethered β,β′-disubstituted nitroolefin. This key carbon–carbon bond forming reaction efficiently constructed a chiral bicyclic core in near-perfect enantio- and diastereo-selectivity, concurrently established three stereogenic centers, including a quaternary carbon, and proved highly scalable. Furthermore, the pathway and origins of enantioselectivity in this catalytic cyclization were probed using density functional theory (DFT) calculations, which revealed the crucial substrate/catalyst interactions in the enantio-determining step. Following construction of the bicyclic core, the total synthesis of madangamine E could be completed, with key steps including a mild one-pot oxidative lactamization of an amino alcohol, a two-step Z-selective olefination of a sterically hindered ketone, and ring-closing metatheses to install the two macrocyclic rings.

The PIFA-initiated oxidative cyclization of 2-(3-butenyl)quinazolin-4(3H)-ones - an efficient approach to 1-(hydroxymethyl)-2,3-dihydropyrrolo[1,2-a]quinazolin-5(1H)-ones

A regioselective method for the synthesis of 1-(hydroxymethyl)-2,3-dihydropyrrolo[1,2-a]quinazolin-5(1H)-ones - close structural analogs of naturally occurring vasicinone alkaloids - is described. The procedure is based on PIFA-initiated oxidative 5-exo-trig cyclization of 2-(3-butenyl)quinazolin-4(3Н)-ones, in turn prepared by thermal cyclocondensation of the corresponding 2-(pent-4-enamido)benzamides. The products obtained have a good natural product likeness (NPL) score and therefore can be useful for the design of natural product-like compound libraries.

Recent progress on the total syntheses of macrocyclic diamine alkaloids

This review highlights the progress and challenges in the chemical synthesis of macrocyclic diamine alkaloids since 2006.

Access to Enantiopure Advanced Intermediates en Route to Madangamines

The synthesis of enantiopure ABCE and ABCD tetracyclic advanced intermediates en route to madangamine alkaloids and studies for the construction of the triunsaturated 15-membered D ring of madangamine B and the saturated 13-membered D ring of madangamine E are reported.

Alkene Difunctionalization Using Hypervalent Iodine Reagents: Progress and Developments in the Past Ten Years

Hypervalent iodine reagents are of considerable relevance in organic chemistry as they can provide a complementary reaction strategy to the use of traditional transition metal chemistry. Over the past two decades, there have been an increasing number of applications including stoichiometric oxidation and catalytic asymmetric variations. This review outlines the main advances in the past 10 years in regard to alkene heterofunctionalization chemistry using achiral and chiral hypervalent iodine reagents and catalysts.

Enantioselective formal synthesis of (+)-madangamine A

A formal synthesis of (+)-madangamine A from phenylglycinol-derived lactam 1, involving the final closure of the peripheral rings from the skipped polyunsaturated diazatricyclic derivative 19, is reported.