Synthesis of the C9-C25 Subunit of Spirastrellolide B

Stereo- and Site-Selective Crotylation of Alcohol Proelectrophiles via Ruthenium-Catalyzed Hydrogen Auto-Transfer Mediated by Methylallene and Butadiene

Iodide-bound ruthenium-JOSIPHOS complexes catalyze the redox-neutral C-C coupling of primary alcohols with methylallene (1,2-butadiene) or 1,3-butadiene to form products of anti-crotylation with good to excellent levels of diastereo- and enantioselectivity. Distinct from other methods, direct crotylation of primary alcohols in the presence of unprotected secondary alcohols is possible, enabling generation of spirastrellolide B (C9-C15) and leucascandrolide A (C9-C15) substructures in significantly fewer steps than previously possible.

An Iterative Phosphate Tether Mediated Approach for the Synthesis of Complex Polyol Subunits

A pot-economical approach to advanced polyol subunits is reported. The key reactions involved are iterative use of a phosphate tether-mediated one-pot sequential RCM/CM/H₂ with subsequent utilization of either a regio-/diasteroselective cuprate addition or a Pd-catalyzed reductive allylic transposition. This method highlights the asymmetric synthesis of 12 complex polyol subunits in 4-6 one-pot sequential operations with a total of 12-14 reactions, of which 4-5 are catalytic, with minimal workup and purification procedures.

Ene-Yne Metathesis of Allylphosphonates and Allylphosphates: Synthesis of Phosphorus-Containing 1,3-Dienes

A variety of ene-yne cross metathesis reactions were performed using unsaturated phosphonate and phosphate reagents, affording the corresponding phosphorylated 1,3-diene products in good to excellent yields. These difficult ene-yne metatheses employed a Grubbs catalyst bearing a cyclic amino alkyl carbene ligand. A variety of terminal alkynes of varying substitution underwent the reaction, and different phosphorus-containing alkenes were found to give the conjugated diene products in high yields. The resulting dienes were further transformed by Horner-type Wittig reactions and a Diels-Alder cycloaddition.

Synthesis and Biological Evaluation of the Southern Hemisphere of Spirastrellolide A and Analogues

The synthesis and biological evaluation of truncated spirastrellolide A analogues comprised of the southern hemisphere against protein phosphatase 2A are described. A convergent synthesis was designed featuring two gold-catalyzed cyclization reactions, specifically, a dehydrative cyclization of monoallylic diols for the synthesis of the tetrahydropyran (A-ring) and a regioselective spiroketalization for the efficient generation of the [6,6]-spiroketal (B, C-ring system). The synthesis of the southern hemisphere of spirastrellolide A was achieved involving the longest linear sequence of 19 steps. A total of eight spirastrellolide A analogues were synthesized, and preliminary PP2A enzyme assay inhibition studies were performed for the first time on analogues of the southern hemisphere. Several analogues showed inhibition, which is a positive indication and perhaps suggests that the unsaturated spiroketal fragment might be crucial to induce PP2A inhibition.

Synergistic approach to polycycles through Suzuki-Miyaura cross coupling and metathesis as key steps

This account provides an overview of recent work, including our own contribution dealing with Suzuki–Miyaura cross coupling in combination with metathesis (or vice-versa). Several cyclophanes, polycycles, macrocycles, spirocycles, stilbenes, biaryls, and heterocycles have been synthesized by employing a combination of Suzuki cross-coupling and metathesis. Various popular reactions such as Diels–Alder reaction, Claisen rearrangement, cross-metathesis, and cross-enyne metathesis are used. The synergistic combination of these powerful reactions is found to be useful for the construction of complex targets and fulfill synthetic brevity.

P-Tether-Mediated, Iterative SN2'-Cuprate Alkylation Strategy to Skipped Polyol Stereotetrads: Utility of an Oxidative "Function Switch" with Phosphite-Borane Tethers

The development of a P-tether-mediated, iterative S_N2'-cuprate alkylation protocol for the formation of 1,3-skipped polyol stereotetrads is reported. This two-directional synthetic strategy builds molecular complexity from simple, readily prepared C₂-symmetric dienediols and unites the chemistry of both temporary phosphite-borane tethers and temporary phosphate tethers-through an oxidative "function switch" of the P-tether itself-to generate intermediates that were previously inaccessible via either method alone.

P-Stereogenic Bicyclo[4.3.1]phosphite Boranes: Synthesis and Utility of Tunable P-Tether Systems for the Desymmetrization of C2-Symmetric 1,3-anti-Diols

The development of P-stereogenic bicyclo[4.3.1]phosphite borane tether systems for the desymmetrization of C₂-symmetric dienediols is reported. This report highlights preliminary studies including tether installation and removal as well as chemoselective functionalization of the exocyclic olefin via diimide reduction or cross-metathesis. Most notably, a divergent oxidation strategy allows for the transformation of the bicyclic phosphite borane complexes to the corresponding phosphate or thiophosphate systems, highlighting the electronic attenuation of this P-tether system.

Phospha-Michael addition reaction of maleimides employing N-heterocyclic phosphine-thiourea as a phosphonylation reagent: synthesis of 1-aryl-2,5-dioxopyrrolidine-3-yl-phosphonate derivatives

The phospha-Michael addition reaction of maleimides with NHP-thiourea under catalyst and additive free conditions has been developed for desymmetrization of maleimides.