Synthesis of fused bicyclic rings by tandem radical ring expansion/cyclization: Evaluating competing intramolecular reactions

Total Synthesis of Panaginsene

The total synthesis of panaginsene has been accomplished in 11 linear steps starting from methyl 3,3-dimethyl-5-oxocyclopent-1-ene-1-carboxylate. The key steps are a Sharpless asymmetric epoxidation and Ti(III)-mediated reductive epoxide opening-radical cyclization to construct the chiral quaternary carbon stereocenter followed by a very challenging HWE olefination reaction on an 1,3-keto aldehyde and a late stage McMurry olefination using low valent titanium to construct the highly constrained angular tetrasubstituted olefin in a five-membered ring.

Changing the path of least resistance, or access to endo-dig products via a sequence of three exo-trig transition states: electronic effects in homoallyic ring expansion cascades of alkenyl isonitriles

Substituent effects reshape the potential energy surfaces for radical homoallylic expansion/fragmentation cascades that transform alkenyl isonitriles into N-heteroaromatics

Studies towards a greener diazo transfer methodology

A mild, efficient and green method has been developed for diazo transfer to β-ketoesters using polystyrene-supported benzenesulfonyl azide, water as solvent and catalytic base.

Coupling cyclizations with fragmentations for the preparation of heteroaromatics: quinolines from o-alkenyl arylisocyanides and boronic acids

Stereoelectronic restrictions on homoallylic ring expansion in alkyne cascades can be overcome by using alkenes as synthetic equivalents of alkynes in reaction cascades that are terminated by C–C bond fragmentation.

Structure-activity relationship and in vitro and in vivo evaluation of the potent cytotoxic anti-microtubule agent N-(4-methoxyphenyl)-N,2,6-trimethyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-4-aminium chloride and its analogues as antitumor agents

A series of 21 substituted cyclopenta[d]pyrimidines were synthesized as an extension of our discovery of the parent compound (±)-1·HCl as an anti-microtubule agent. The structure-activity relationship indicates that the N-methyl and a 4N-methoxy groups appear important for potent activity. In addition, the 6-substituent in the parent analogue is not necessary for activity. The most potent compound 30·HCl was a one to two digit nanomolar inhibitor of most tumor cell proliferations and was up to 7-fold more potent than the parent compound (±)-1·HCl. In addition, 30·HCl inhibited cancer cell proliferation regardless of Pgp or βIII-tubulin status, both of which are known to cause clinical resistance to several anti-tubulin agents. In vivo efficacy of 30·HCl was demonstrated against a triple negative breast cancer xenograft mouse model. Compound 30·HCl is water-soluble and easily synthesized and serves as a lead compound for further preclinical evaluation as an antitumor agent.

Photoinduced electron transfer promoted radical ring expansion and cyclization reactions of α-(ω-carboxyalkyl) β-keto esters

Photoinduced electron transfer (PET) promoted decarboxylation of α-(ω-carboxyalkyl) β-keto esters undergoes radical ring expansion and cyclization reactions. This mild and environmentally friendly method can provide one-carbon expanded γ-keto esters and bicyclic alcohols, and the product distribution is strongly dependent on the length of the alkyl chain containing the terminal carboxylate group.

Synthesis of the bridging framework of phragmalin-type limonoids

An efficient synthesis of the octahydro-1H-2,4-methanoindene core of phragmalin-type limonoids, such as xyloccensins O and P, is reported. The success of the synthetic route is predicated on the use of network analysis in the retrosynthetic analysis and a Diels-Alder reaction for the synthesis of a key hydrindanone derivative.

Sequential Ru-Pd catalysis: a two-catalyst one-pot protocol for the synthesis of N- and O-heterocycles

An atom economic, selective, and highly practical two-metal one-pot synthesis of heterocycles has been developed that efficiently affords enantio- and diastereopure N- and O-heterocyclic products. Furthermore, use of a chiral catalyst in the two-metal procedure allows formation of all possible diastereomers, even those that are traditionally difficult to access via cyclization routes due to thermodynamics. Interestingly, the nature of the enantiodiscriminating event differs between the use of amine versus alcohol nucleophiles. The method also affords heterocyclic products that are synthetically useful intermediates. Through the Z-vinylsilane a variety of stereodefined trisubstituted olefin products can be accessed including several all-carbon motifs. Finally, the utility of these heterocyclic products in total synthesis is demonstrated through concise syntheses of a kainoid intermediate, a constituent of oil of rose, and the ring B portion of bryostatin, a potent chemotherapeutic.