Iodocyclization and Prins-Type Macrocyclization: An Efficient Formal Synthesis of Leucascandrolide A

Total Synthesis and Determination of Absolute Configuration of Cryptorigidifoliol G

The first asymmetric total synthesis of (1S,5R,7S)-cryptorigidifoliol G and (1S,5R,7R)-cryptorigidifoliol G of the proposed natural product was achieved. The key steps in the synthesis involved Keck-Maruoka allylation, our own developed protocol for the construction of the trans-2,6-disubstituted dihydropyran, iodolactonization, cross-metathesis, Prins cyclization, and cis-Wittig olefination reaction. A comparison of the NMR as well as analytical data and thorough analysis of the 2D NMR suggested that the absolute stereochemistry of the proposed natural product is (1S,5R,7S)-cryptorigidifoliol G.

Scalable Total Synthesis of Leucascandrolide A Macrolactone Using a Chiral Phosphoric Acid/CuX Combined Catalytic System

A scalable total synthesis of leucascandrolide A macrolactone has been accomplished with a longest linear sequence of 17 steps from readily available feedstocks in 31.2% yield. The key steps in this synthesis are the enantioselective allylation reaction by chiral phosphoric acid (CPA)/CuBr cooperative catalysis and the diastereoselective catalytic crotylation in the presence of CPA with CuCl. These catalytic reactions can be performed on a gram scale to afford the desired products with excellent stereoselectivities.

BF3·OEt2-Catalyzed Unexpected Stereoselective Formation of 2,4-trans-Diallyl-2-methyl-6-aryltetrahydro-2H-pyrans with Quaternary Stereocenters

The present manuscript describes a convenient, mild, and highly stereoselective method for the allylation of δ-hydroxy-α,β-unsaturated ketones having a benzylic hydroxyl group at the δ-position using allyltrimethylsilane mediated by BF₃·OEt₂, leading to 2,4-diallyl-2-methyl-6-aryltetrahydro-2H-pyran ring systems with quaternary carbon stereogenic centers. This represents the first example of a tandem isomerization followed by one C-O and two C-C bond-forming reactions in one pot. The isolation of TMS-protected lactol as an intermediate from the reaction strongly supports the proposed mechanistic pathway.

CuBr2-catalyzed diastereoselective allylation: total synthesis of decytospolides A and B and their C6-epimers

An efficient CuBr₂-catalyzed diastereoselective allylation of a cyclic hemiacetal with allyltrimethylsilane as a nucleophile has been developed. The protocol offers a cost effective, protecting group tolerant, and operationally simple approach to 2,6-trans-disubstituted tetrahydropyran with excellent diastereoselectivity. Furthermore, the application of this methodology has been demonstrated in the total synthesis of decytospolides A and B and their C6-epimers.

The Mukaiyama type aldol reaction for the synthesis of trans-2,6-disubstituted tetrahydropyrans: synthesis of diospongin A and B

An efficient synthesis protocol for the preparation of trans-2,6-disubstituted tetrahydropyrans by the reaction of 1-phenyl-1-triemthylsiloxyethylene with six membered cyclic hemiacetals in the presence of iodine is developed. This reaction proceeds smoothly under mild conditions employing a catalytic amount of molecular iodine. The feature of this novel conversion includes milder reaction conditions, broader substrate scope, functional group tolerance and good diastereoselectivity. The efficiency and practicality of the current method were successfully displayed in the total synthesis of diospongin A and B in good yields.

An efficient iodine pentoxide-triggered iodocarbocyclization for the synthesis of iodooxindoles in water

An efficient iodocarbocyclization of alkenes for the synthesis of iodooxindoles has been developed. This reaction proceeds in a chemoselective manner and shows excellent tolerance of various functional groups, including a chemosensitive hydroxymethyl group. Nonmetal inorganic iodine pentoxide was used as both the oxidant and iodine source, making this protocol very practical. On the basis of experimental observations, a plausible electrophilic reaction mechanism was proposed.

Stereoconfining macrocyclizations in the total synthesis of natural products

This review covers selected examples of point chirality-forming macrocyclizations in natural product total synthesis in the past three decades.

A synthetic study toward the core structure of (-)-apicularen A

A concise synthetic strategy towards the core structure of (-)-apicularen A has been described in an 11-step synthetic sequence from a known intermediate. The key steps include tandem isomerization followed by C-O and C-C bond-forming reactions and iodocyclization strategies for the synthesis of a bicyclic ether embedded in the macrolactone ring. The applied reagent-controlled Keck-Maruoka allylation, Lin Pu alkynylation and Ricket-Diels-Alder reactions were used to simplify the synthetic sequence of related natural products. An intramolecular Yamaguchi lactonization constructed the macrolactone core, while the attempt to install the C11 hydroxyl chiral centre either under catalytic hydrogenation conditions or oxidative conditions was not successful.

Studies toward the synthesis of strevertenes A and G: stereoselective construction of C1–C19segments of the molecules

Efficient route for the stereoselective synthesis of common C₁–C₁₉segment of strevertenes A and G has been developed.

Approach to the Synthesis of the C1-C11 and C14-C18 portion of Leucascandrolide A

An asymmetric synthesis of the C1 to C11 and C14 to C18 fragments of the macrocyclic portion of the antibiotic Leucascandrolide A was achieved in 21 total steps from an achiral dienoate. The key 4-hydroxy-2,5-pyran portion of the natural product was established by oxy-Michael cyclization of a 5,7,9,11-tetraol intermediate, which in turn was established by an iterative asymmetric-hydration of dienoates. Alternative strategies for establishing the polyol stereochemistry were explored.

Gold-catalyzed diastereoselective synthesis of 2,6-trans-disubstituted tetrahydropyran derivatives: application for the synthesis of the C1–C13 fragment of bistramide A and B

An efficient Au(iii)-catalyzed diastereoselective allylation leading to 2,6-trans-disubstituted tetrahydropyrans and application for the synthesis of the C1–C13 fragment of bistramide A and B is described.

Studies for the enantiocontrolled preparation of substituted tetrahydropyrans: Applications for the synthesis of leucascandrolide A macrolactone

Strategies for the stereocontrolled preparations of 2,6-cis-and 2,6-trans-substituted tetrahydropyrans have been devised. These studies have explored methodology for asymmetric induction in SE' reactions using chiral 1,3,2-diazaborolidine controllers. Reactions with aldehydes at -78 °C yield nonracemic 1,5-diols for chemoselective internal backside displacements. This concept is developed as a flexible and reliable strategy in studies toward leucascandrolide A macrolactone 2 via the sequential applications of SE' reactions leading to the C1-C9 aldehyde 14, and the bis-tetrahydropyran 59, respectively.

Total synthesis of bryostatin 9

The total synthesis of bryostatin 9 was accomplished using a uniquely step-economical and convergent Prins-driven macrocyclization strategy. At 25 linear and 42 total steps, this is currently the most concise and convergent synthesis of a potent bryostatin.