Michael P. Jennings

Total Synthesis of (−)-Dactylolide and Formal Synthesis of (−)-Zampanolide via Target Oriented β-C-Glycoside Formation

The total synthesis of (-)-dactylolide and formal synthesis of (-)-zampanolide via target oriented beta-C-glycoside formation is described. The two key reactions involved a stereoselective reduction of the appropriate oxocarbenium cation and a highly chemo- and diastereoselective ring-closing metathesis protocol for the formation of the macrocyclic core. In addition to the described chemistry, in vitro screening of the antipode of natural dactylolide against the NCIs 60 cancer cell line helped to illuminate the critical importance of the N-acyl hemiaminal side chain of natural zampanolide for its reported potent nanomolar cytotoxicities. Furthermore, by means of the in vitro screen of (-)-dactylolide, a promising cancer therapeutic lead has now emerged for a variety of carcinomas. More specifically, (-)-dactylolide exhibited GI50 values in the nanomolar (25-99 ng/mL) range against the four cell lines HL-60, K-562, HCC-2998, and SF-539, while displaying modest LC50 values.

An expedient entry into the fused polycyclic skeleton of vannusal AElectronic supplementary information (ESI) available: selected physical data for compounds 11 and 2. See http://www.rsc.org/suppdata/cc/b2/b208234a/Dedicated to Professor Herbert C. Brown on the occasion of his 90th birthday.

The synthesis of the fused polycyclic carbon framework of vannusal A is described; key features include inter- and intramolecular aldol reactions, a Mn(III) initiated radical cyclization, and a ring-closing olefin metathesis reaction.

An efficient formal synthesis of (-)-clavosolide a featuring a "mismatched" stereoselective oxocarbenium reduction.

The enantioselective formal synthesis of the polyketide marine natural product (-)-clavosolide A is presented. The construction of the beta-C-glycoside subunit is highlighted by a one-pot oxocarbenium cation formation/reduction sequence. Yamaguchi dimerization afforded the diolide aglycon in 18 steps (longest linear sequence).

Convergent Formal Syntheses of (±)-Brussonol and (±)-Abrotanone via an Intramolecular Marson-Type Cyclization

The formal convergent syntheses of both (+/-)-brussonol and (+/-)-abrotanone are reported. The key step involved the diastereoselective capture of an in situ generated oxocarbenium cation via an intramolecular Friedel-Crafts/Marson-type cyclization.

An efficient 1,2-chelation-controlled reduction of protected hydroxy ketones via Red-Al.

In this paper, we have demonstrated that Red-Al is an efficient chelation-controlled reducing reagent for acyclic acetal (i.e., MOM, MEM, SEM, and BOM) protected alpha-hydroxy ketones. Typically, diastereomeric ratios (dr) ranged from 5 to 20:1 for the 1,2- anti-diols in good to excellent yields.

High-Spin Ribbons and Antiferromagnetic Ordering of a Mn II - Biradical-Mn II Complex

A binuclear metal coordination complex of the first thiazyl-based biradical ligand 1 is reported (1 = 4,6-bis(1,2,3,5-dithiadiazolyl)pyrimidine; hfac =1,1,1,5,5,5,-hexafluoroacetylacetonato-). The Mn(hfac)2-biradical-Mn(hfac)2 complex 2 is a rare example of a discrete, molecular species employing a neutral bridging biradical ligand. It is soluble in common organic solvents and can be easily sublimed as a crystalline solid. Complex 2 has a spin ground state of S(T) = 4 resulting from antiferromagnetic coupling between the S(birad) = 1 biradical bridging ligand and two S(Mn) = 5/2 Mn(II) ions. Electrostatic contacts between atoms with large spin density promote a ferromagnetic arrangement of the moments of neighboring complexes in ribbon-like arrays. Weak antiferromagnetic coupling between these high-spin ribbons stabilizes an ordered antiferromagnetic ground state below 4.5 K. This is an unusual example of magnetic ordering in a molecular metal-radical complex, wherein the electrostatic contacts that direct the crystal packing are also responsible for providing an efficient exchange coupling pathway between molecules.

Total Synthesis of 7-Deoxy-6-O-methylfusarentin Featuring a Chelation-Controlled 1,3-Reetz–Keck-Type Allylation

The total synthesis of 7-deoxy-6-O-methylfusarentin (1) and a formal synthesis of 7-deoxy-6,8-O-dimethylfusarentin (2) has been successfully achieved in 10 steps. The described tactic underscores a diastereoselective strategy which incorporates a single acyclic reaction based on the initial stereocenter by means of a 1,3-chelation-controlled Reetz-Keck-type allylation.

Syntheses of (−)-Cryptocaryolone and (−)-Cryptocaryolone Diacetate via a Diastereoselective Oxy-Michael Addition and Oxocarbenium Allylation

The total syntheses of both (-)-cryptocaryolone and (-)-cryptocaryolone diacetate is presented herein. The usage of a diastereoselective oxy-Michael addition/benzylidene acetal formation coupled with a selective axial oxocarbenium allylation allowed for the preparation of the α-C-glycoside moiety present in the bicyclic bridged structure. In addition, the syn-1,3-diol of the linear portion was installed via a Wacker oxidation followed by a subsequent directed reduction of the appropriate homoallylic alcohol precursor.

Trinuclear Mn(II) complex with paramagnetic bridging 1,2,3-dithiazolyl ligands

The first metal coordination complex of a radical ligand based on the 1,2,3-dithiazolyl heterocycle is reported. 6,7-Dimethyl-1,4-dioxo-naphtho[2,3-d][1,2,3]dithiazolyl acts as a bridging ligand in the volatile trinuclear Mn(hfac)(2)-Rad-Mn(hfac)(2)-Rad-Mn(hfac)(2) complex (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The Mn(II) and radical ligand spins are coupled anti-ferromagnetically (AF) resulting in an S(T) = 13/2 spin ground state.

Vicinal functionalization of propiolate esters via a tandem catalytic carbocupration-Mukaiyama aldol reaction sequence.

The vicinal functionalization of propiolate esters via a tandem catalytic carbocupration-Mukaiyama aldol reaction sequence has been investigated. It has been shown that catalyst loadings as low as 8 mol % readily allow for good yields and excellent diastereoselectivities (>20:1) for a series of Grignard reagents and aldehydes.