Divergent Strategies for the π-Extension of Heteroaryl Halides Using Norbornadiene as an Acetylene Synthon.

Pd-catalyzed multicomponent coupling reactions of five-membered heteroaryl halides and norbornadiene (NBD) were developed. Either direct addition of (benzo)azoles or 2:1 annulation was achieved depending on the propensity of the intermediate complex to undergo palladacycle formation, determined by the nature and substitution pattern of the heteroarene. The obtained exo- and cis-diheteroaryl norbornenes underwent epimerization and retro-Diels-Alder reactions to afford the corresponding trans-isomers and π-extended heteroaromatic systems, respectively, demonstrating the versatility of NBD as an acetylene synthon.

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.

Total Synthesis of Four Isomers of the Proposed Structures of Cryptorigidifoliol K.

The first asymmetric convergent total synthesis of four isomers of proposed structures of cryptorigidifoliol K (1a, 1b, 1c, and 1d) has been achieved from commercially available starting materials. The key steps in this synthesis involve tandem isomerization followed by a C-O and C-C bond-forming reaction for the construction of trans-2,6-disubstituted dihydropyran, iodolactonization, isomerization of terminal alkene, and cross-metathesis reaction. The large discrepancies in the spectroscopic data (1H NMR) of synthetic cryptorigidifoliol K from the natural product suggest that the structure of the natural cryptorigidifoliol K requires revision.

Total Synthesis of Tetraketide and Cryptorigidifoliol I via a Sequential Allylation Strategy.

A unified and efficient synthetic route for both tetraketide (1) and cryptorigidifoliol I (2) has been devised successfully from commercially available starting materials in 11 and 17 steps, with 16% and 11% overall yields, respectively. Highlights of the syntheses involved sequential Lewis acid-catalyzed highly regio- and diastereoselective allylations and intramolecular Mitsunobu lactonization.

Highly stereocontrolled synthesis of trans-2,6-disubstituted-5-methyl-3,6-dihydropyrans: stereoselective synthesis of the bicyclic core of penostatin B.

An efficient, mild, and highly diastereoselective strategy for the synthesis of trans-2,6-disubstituted-5-methyl-3,6-dihydropyran ring systems has been developed starting from δ-hydroxy α-methyl α,ß-unsaturated aldehydes and allyltrimethylsilane in the presence of a catalytic amount of ZnBr2 in a highly diastereoselective manner with excellent yield. The versatility of the above method was also demonstrated for the construction of the bicyclic core present in penostatin B in a concise and highly stereoselective manner.