Asymmetric total synthesis of the myxobacteria metabolites crocacins A–D

Stereoselective Semi-Hydrogenations of Alkynes by First-Row (3d) Transition Metal Catalysts

The chemo- and stereoselective semi-hydrogenation of alkynes to alkenes is a fundamental transformation in synthetic chemistry, for which the use of precious 4d or 5d metal catalysts is well-established. In mankind's unwavering quest for sustainability, research focus has considerably veered towards the 3d metals. Given their high abundancy and availability as well as lower toxicity and noxiousness, they are undoubtedly attractive from both an economic and an environmental perspective. Herein, we wish to present noteworthy and groundbreaking examples for the use of 3d metal catalysts for diastereoselective alkyne semi-hydrogenation as we embark on a journey through the first-row transition metals.

Design and synthesis of novel monoterpenoid indole alkaloid-like analogues and their antitumour activities in vitro

34 novel monoterpenoid indole alkaloid analogues were synthesized based on combinatorial chemistry strategy. Compound 18 was found to be the most promising antitumour lead compound.

Catalyst-controlled stereoselective olefin metathesis as a principal strategy in multistep synthesis design: a concise route to (+)-neopeltolide

Molybdenum-, tungsten-, and ruthenium-based complexes that control the stereochemical outcome of olefin metathesis reactions have been recently introduced. However, the complementary nature of these systems through their combined use in multistep complex molecule synthesis has not been illustrated. A concise diastereo- and enantioselective route that furnishes the anti-proliferative natural product neopeltolide is now disclosed. Catalytic transformations are employed to address every stereochemical issue. Among the featured processes are an enantioselective ring-opening/cross-metathesis promoted by a Mo monoaryloxide pyrrolide (MAP) complex and a macrocyclic ring-closing metathesis that affords a trisubstituted alkene and is catalyzed by a Mo bis(aryloxide) species. Furthermore, Z-selective cross-metathesis reactions, facilitated by Mo and Ru complexes, have been employed in the stereoselective synthesis of the acyclic dienyl moiety of the target molecule.

Total synthesis of the endogenous inflammation resolving lipid resolvin D2 using a common lynchpin

The total synthesis of the endogenous inflammation resolving eicosanoid resolvin D2 (1) is described. The key steps involved a Wittig reaction between aldehyde 5 and the ylide derived from phosphonium salt 6 to give enyne 17 and condensation of the same ylide with aldehyde 7 to afford enyne 11. Desilylation of 11 followed by hydrozirconation and iodination gave the vinyl iodide 4 and Sonogashira coupling between this compound and enyne 3 provided alkyne 18. Acetonide deprotection, partial reduction and ester hydrolysis then gave resolvin D2 (1).

Step-economic synthesis of (+)-crocacin C: a concise crotylboronation/[3,3]-sigmatropic rearrangement approach

The step-economic total synthesis of (+)-crocacin C has been achieved in 20% yield from commercially available starting materials. This approach requires the isolation of only 8 intermediates and can provide a reliable supply of (+)-crocacin C for the development of new antifungal and crop protection agents.

Synthesis of myxobacteria metabolites

Myxobacteria are an excellent source of novel secondary metabolites with a range of biological activities. This review details the synthesis of several examples of these natural products. The total synthesis of all the members of the crocacin family is presented where the stereochemistry of the stereotetrad was set via a tin-mediated syn-aldol reaction followed by selective anti-reduction. The other key step in the route to crocacins A, B, and D was the introduction of the enamide functionality by acylation of an enecarbamate. A formal synthesis of apicularen A is also discussed, which involved a base-induced macrolactonization reaction and a transannular oxy-Michael cyclization to secure the tetrahydropyran ring. Finally, the total synthesis of deshydroxyajudazol B is summarized. This route details a modified approach to the 2,4-disubstituted oxazole, and a Diels–Alder reaction followed by aromatization was utilized to form the isochromanone moiety. A highly efficient Sonogashira coupling followed by partial reduction then gave deshydroxyajudazol B.

Enantioselective synthesis of (+)-crocacin C. An example of a highly challenging mismatched double asymmetric δ-stannylcrotylboration reaction

A concise, enantioselective synthesis of (+)-crocacin C is described, featuring a highly diastereoselective mismatched double asymmetric δ-stannylcrotylboration of the stereochemically demanding chiral aldehyde 9 with the bifunctional crotylborane reagent (S)-E-10. The total synthesis of (+)-crocacin C was accomplished in seven steps (longest linear sequence) starting from commercially available precursors.