Jonathan T. Reeves

Organometallic methods for the synthesis and functionalization of azaindoles

Azaindoles (also called pyrrolopyridines) constitute essential subunits in many pharmaceutically important compounds. The synthesis of azaindoles has been a great synthetic challenge for chemists. Many classical methods for indole synthesis (such as Fischer and Madelung cyclizations) often cannot be effectively applied to the synthesis of the corresponding azaindoles. In recent years, advances in organometallic chemistry have enabled a number of novel and efficient methodologies for azaindole formation as well as for the further functionalization of azaindole templates. In this tutorial review, we have surveyed the recent development of organometallic chemistry-based methods for azaindole synthesis.

Copper Catalyzed Asymmetric Propargylation of Aldehydes

The highly enantio- and regioselective copper catalyzed asymmetric propargylation of aldehydes with a propargyl borolane reagent is reported. The methodology demonstrated broad functional group tolerance and provided high enantioselectivities for aliphatic, vinyl, and aryl aldehydes. The utility of the TMS homopropargylic alcohols was demonstrated by the facile conversion to a chiral dihydropyranone.

Room Temperature Palladium-Catalyzed Cross Coupling of Aryltrimethylammonium Triflates with Aryl Grignard Reagents

Aryltrimethylammonium triflates and tetrafluoroborates were found to be highly reactive electrophiles in the Pd-catalyzed cross coupling with aryl Grignard reagents. The coupling reactions proceed at ambient temperature with a nearly stoichiometric quantity of Grignard reagent, and diverse functionality is tolerated. Competition experiments established the reactivity of PhNMe(3)OTf relative to PhCl, PhBr, PhI, and PhOTf.

Efficient asymmetric synthesis of P-chiral phosphine oxides via properly designed and activated benzoxazaphosphinine-2-oxide agents.

A general, efficient, and highly diastereoselective method for the synthesis of structurally and sterically diverse P-chiral phosphine oxides was developed. The method relies on sequential nucleophilic substitution on the versatile chiral phosphinyl transfer agent 1,3,2-benzoxazaphosphinine-2-oxide, which features enhanced and differentiated P-N and P-O bond reactivity toward nucleophiles. The reactivities of both bonds are fine-tuned to allow cleavage to occur even with sterically hindered nucleophiles under mild conditions.

The Reaction of Grignard Reagents with Bunte Salts: A Thiol-Free Synthesis of Sulfides

S-Alkyl, S-aryl, and S-vinyl thiosulfate sodium salts (Bunte salts) react with Grignard reagents to give sulfides in good yields. The S-alkyl Bunte salts are prepared from odorless sodium thiosulfate by an SN2 reaction with alkyl halides. A Cu-catalyzed coupling of sodium thiosulfate with aryl and vinyl halides was developed to access S-aryl and S-vinyl Bunte salts. The reaction is amenable to a broad structural array of Bunte salts and Grignard reagents. Importantly, this route to sulfides avoids the use of malodorous thiol starting materials or byproducts.

Chemistry and Biology of Curacin A

Many natural and synthetic compounds bind to tubulin, an ubiquitous globular protein that provides the building blocks for the cellular microtubule network that controls chromosome segregation during mitosis, vesicle movements, intracellular transport of organelles, ciliar and flagellar movement, and maintenance of cell shape. Since the isolation of the antimitotic marine natural product curacin A in 1994, synthetic work on this colchicine-site binding agent has been intense, but only recently have synthetic derivatives been identified that match its potency for tubulin polymerization inhibition and its high level of growth inhibition in cancer cell lines. In addition to several total synthesis efforts, combinatorial libraries were constructed using solution phase and fluorous scavenging approaches. Low water-solubility and lack of chemical stability represent strong detriments for the clinical development of curacin A, but synthetic analogs with improved bioavailability might ultimately probe the paradigm for anticancer efficacy of colchicine-site tubulin binding agents.

Synthesis and applications of a fluorous THP protective group

A recyclable fluorous labeled THP protecting group has been developed that allows for simple purification of small molecules by liquid-liquid extraction with FC-72/MeCN, and of larger or more polar molecules by solid phase extraction with fluorous reverse phase silica gel. In addition, we report a new glycosylation method which uses the Cp2ZrCl2AgClO4 reagent system to activate an anomeric sulfoxide.

Total Synthesis of Phorboxazole A

In 1995 Searle and Molinski reported the isolation of phorboxazoles A ( 1) and B (2), isomeric oxazole-containing macrolides, from the marine sponge Phorbas sp. endemic to the western coast of Australia (Scheme 1). 1 The relative and absolute stereochemistries of the phorboxazoles were secured via a combination of NMR analysis, degradation studies, and synthetic correlation. 2 When tested against the NCI panel of 60 human tumor cell lines, the phorboxazoles displayed virtually unsurpassed cytotoxicity, exhibiting a mean GI 50 of 1.58× 10-9 M. Although the exact mechanism of action remains unknown, studies demonstrate that phorboxazole A ( 1) arrests the cell cycle at the S phase and does not affect tubulin. Given the potent cytotoxicity and the possibility of a new mechanism of action, the phorboxazoles were selected by the NCI for in vivo trials. 2a

Copper-catalyzed annulation of 2-formylazoles with o-aminoiodoarenes.

In the presence of catalytic CuI and sparteine, 2-formylpyrroles can be annulated with o-aminoiodoarenes to give substituted pyrrolo[1,2-a]quinoxalines and related heterocycles. The reaction also works for annulation of 2-formylindoles, 2-formylimidazole, 2-formylbenzimidazole, and a 3-formylpyrazole.

N-Heterocyclic Carbene-Catalyzed Silyl Enol Ether Formation†

N-Heterocyclic carbenes (NHCs) were found to catalyze the silyl transfer from trialkylsilyl ketene acetals to ketones. In the presence of a catalytic amount of NHC 3 (IAd, 0.1 to 5 mol %), a series of enolizable ketones as well as cyclohexanecarboxaldehyde were efficiently converted into the corresponding silyl enol ethers at 23 degrees C in THF.