Convergent and Biomimetic Enantioselective Total Synthesis of (-)-Communesin F

The first biomimetic enantioselective total synthesis of (-)-communesin F based on a late-stage heterodimerization and aminal exchange is described. Our synthesis features the expedient diazene-directed assembly of two advanced fragments to secure the congested C3a-C3a' linkage in three steps, followed by a highly efficient biogenetically inspired aminal reorganization to access the heptacyclic communesin core in only two additional steps. Enantioselective syntheses of the two fragments were developed, with highlights including the catalytic asymmetric halocyclization and diastereoselective oxyamination reactions of tryptamine derivatives, a stereoselective sulfinimine allylation, and an efficient cyclotryptamine-C3a-sulfamate synthesis by either a new silver-promoted nucleophilic amination or a rhodium-catalyzed C-H amination protocol. The versatile syntheses of the fragments, their stereocontrolled assembly, and the efficient aminal exchange as supported by in situ monitoring experiments, in addition to the final stage N1'-acylation of the communesin core, provide a highly convergent synthesis of (-)-communesin F.

Application of diazene-directed fragment assembly to the total synthesis and stereochemical assignment of (+)-desmethyl-meso-chimonanthine and related heterodimeric alkaloids

We describe the first application of our methodology for heterodimerization via diazene fragmentation towards the total synthesis of (-)-calycanthidine, meso-chimonanthine, and (+)-desmethyl-meso-chimonanthine. Our syntheses of these alkaloids feature an improved route to C3a-aminocyclotryptamines, an enhanced method for sulfamide synthesis and oxidation, in addition to a late-stage diversification leading to the first enantioselective total synthesis of (+)-desmethyl-meso-chimonanthine and its unambiguous stereochemical assignment. This versatile strategy for directed assembly of heterodimeric cyclotryptamine alkaloids has broad implications for the controlled synthesis of higher order derivatives with related substructures.

A photoisomerization-coupled asymmetric Stetter reaction: application to the total synthesis of three diastereomers of (-)-cephalimysin A

The total synthesis of 8-epi, 8,9-epi, and 9-epi-(-)-cephalimysin A is described. Our catalytic enantioselective synthesis takes advantage of a novel tandem photoisomerization/Stetter reaction. The approach provides rapid access to the desired spirofuranone lactam core in good yield and excellent enantioselectivity. A late stage oxidation strategy allows for flexible access to three of the four diastereomers of cephalimysin A. Access to the epimers provides further support for the correction of the initially proposed relative stereochemistry of cephalimysin A.

Radical-mediated dimerization and oxidation reactions for the synthesis of complex alkaloids

Concise and general strategies for radical-based dimerization of cyclotryptamine and cyclotryptophan derivatives in addition to radical-based oxidation of structurally complex diketopiperazines are discussed. The impact of these radical-based chemistries on the rapid generation of molecular complexity is highlighted using representative examples from recent complex homodimeric alkaloid total syntheses. Additionally, a new and general strategy for radical-based directed heterodimerization of cyclotryptamine substructures via solvent-caged unsymmetrical diazene fragmentation is discussed.

Directed heterodimerization: stereocontrolled assembly via solvent-caged unsymmetrical diazene fragmentation

A general strategy for the directed and stereocontrolled assembly of carbon-carbon linked heterodimeric hexahydropyrroloindoles is described. The stepwise union of complex amines in the form of mixed diazenes followed by photoexpulsion of dinitrogen in a solvent cage provides completely guided assembly at challenging C(sp(3))-C(sp(3)) and C(sp(3))-C(sp(2)) connections.

Asymmetric synthesis of functionalized cyclopentanones via a multicatalytic secondary amine/N-heterocyclic carbene catalyzed cascade sequence

A one-pot, asymmetric multicatalytic formal [3+2] reaction between 1,3-dicarbonyls and alpha,beta-unsaturated aldehydes is described. The multicatalytic process involves a secondary amine catalyzed Michael addition followed by a N-heterocyclic carbene catalyzed intramolecular crossed benzoin reaction to afford densely functionalized cyclopentanones with high enantioselectivities. The reaction proceeds with a variety of alkyl and aryl enals as well as a range of 1,3-dicarbonyls (diketones and beta-ketoesters). The functionalized products are obtained from cheap, readily available starting materials in a rapid and efficient manner in a one-pot, one-step operation.

Schiff Base Route to Stackable Pseudo-Triphenylenes: Stereoelectronic Control of Assembly and Luminescence

Tandem tautomerization-trapping of isomeric mixtures of tris(N-salicylideneamine)s facilitated access to a new class of discotic molecules that are geometrically analogous to 2,6,10-trisubstituted triphenylenes. The shape and electrostatic complementarity associated with the molecular C3 symmetry assists cofacial stacking of pi-faces to afford either infinite one-dimensional columns or discrete dimeric capsules. Structural reinforcement achieved by such interlocked geometry resulted in significant fluorescence enhancement upon aggregation in solution, as determined by dynamic light scattering and fluorescence spectroscopy.