Total synthesis of (-)-cylindrocyclophanes A and F exploiting the reversible nature of the olefin cross metathesis reaction.

Efficient total syntheses of the C(2)-symmetric (-)-cylindrocyclophanes A and F (1a and 1f) have been achieved. The initial strategy featured the use of a common advanced intermediate to assemble in stepwise fashion the required macrocycle of 1f, exploiting in turn a Myers reductive coupling followed by ring-closing metathesis. In a second-generation strategy, a remarkable cross olefin metathesis dimerization cascade was discovered and exploited to assemble the requisite [7,7]-paracyclophane macrocycles of both 1a and 1f from dienyl monomers. The successful syntheses also featured the effective use of the Danheiser annulation to construct substrates for both the Myers reductive coupling and the metathesis dimerizations strategies. Finally, the Kowalski two-step chain homologation of esters to siloxyalkynes proved superior over the original one-step protocol.

Efficient stereochemical relay en route to leucascandrolide A.

[structure: see text]. A complete relay of the initial stereochemical information is central to the efficient and highly stereocontrolled construction of the C1-C15 fragment of the marine macrolide leucascandrolide A. Cyclic silane 3, assembled via Pt-catalyzed hydrosilylation, was designed to serve as a temporary template for the installation of the C12 stereogenic center. The strategy features a highly convergent C10-C11 bond construction via 1,5-anti-selective aldol reaction and rapid assembly of the trisubstituted pyran subunit via Prins desymmetrization.

Racemic and asymmetric Diels-Alder reactions of 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes.

Achiral and chiral 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes were prepared from readily available starting materials. Although more stable than the parent 1-amino-3-siloxy dienes, the 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes are still very reactive in Diels-Alder reactions, somewhat more than 1,3-dialkoxy-1, 3-butadienes (e.g., Danishefsky's diene). The cycloadditions of the achiral and chiral dienes with several different dienophiles were examined. The reactions proceeded in good yield, with modest to high endo selectivity. The chiral dienes exhibited excellent facial selectivity in cycloadditions with alpha-substituted acroleins, maleic anhydride and N-phenylmaleimide. Upon reduction and hydrolysis of the cycloadducts, substituted cyclohexenones were obtained with ee's ranging from 22% to >98%.

Regiocontrolled synthesis of carbocycle-fused indoles via arylation of silyl enol ethers with o-nitrophenylphenyliodonium fluoride.

[formula: see text] A new, regiocontrolled synthesis of carbocycle-fused indoles has been developed. The two-step procedure involves first the regiospecific arylation of silyl enol ethers with o-nitrophenylphenyliodonium fluoride (1). Reduction of the nitro group on the aromatic ring with TiCl3 followed by spontaneous condensation of the aniline with the ketone then affords the indole products.