Conversion of Weinreb Amides into Benzene Rings Incorporating the Amide Carbonyl Carbon

New small γ-turn type N-primary amino terminal tripeptide organocatalyst for solvent-free asymmetric aldol reaction of various ketones with aldehydes

New small γ-turn type N-primary amino terminal tripeptides were synthesized and their functionality as an organocatalyst was examined in the asymmetric aldol reaction of various ketones with different aromatic aldehydes under solvent-free neat conditions to afford the desired chiral anti-aldol products in good to excellent chemical yields, diastereoselectivities and enantioselectivities (up to 99%, up to syn : anti/13 : 87 dr, up to 99% ee).

Total syntheses of (±)-penicibilaenes A and B via intramolecular aldol condensation

Concise total syntheses of penicibilaenes A and B were achieved via intramolecular aldol condensation and other key reactions.

Activation of olefins via asymmetric Brønsted acid catalysis

The activation of olefins for asymmetric chemical synthesis traditionally relies on transition metal catalysts. In contrast, biological enzymes with Brønsted acidic sites of appropriate strength can protonate olefins and thereby generate carbocations that ultimately react to form natural products. Although chemists have recently designed chiral Brønsted acid catalysts to activate imines and carbonyl compounds, mimicking these enzymes to protonate simple olefins that then engage in asymmetric catalytic reactions has remained a substantial synthetic challenge. Here, we show that a class of confined and strong chiral Brønsted acids enables the catalytic asymmetric intramolecular hydroalkoxylation of unbiased olefins. The methodology gives rapid access to biologically active 1,1-disubstituted tetrahydrofurans, including (-)-Boivinianin A.

Transformations of terpenes and terpenoids via carbon–carbon double bond metathesis

The review reports on transformations of unsaturated terpenes and terpenoids via olefin metathesis processes including ring closing metathesis of dienes, cross metathesis with functional olefins and ethenolysis, and ring opening metathesis as well as ring opening/cross metathesis.

Direct Access to Fused Salicylaldehydes and Salicylketones from Tetraynes

A facile method for the synthesis of fused, multifunctionalized salicylaldehydes and salicylketones by a one-pot, three-step cascade hexadehydro-Diels-Alder (HDDA) reaction of tetraynes followed by an intermolecular aldehyde/ketone reaction and hydroxylation is reported. Target compounds were prepared by the condensation of malonates with 3-bromo-1-propyne, and the resulting 2,2-di(1-propyn-3-yl)malonates underwent cross-coupling with phenylethynyl bromides to afford 2,2-di(5-phenyl-2,4-pentadiynyl)malonates, which underwent intramolecular cyclization to produce bicyclic salicylaldehydes. The overall transformation involves the formation of four new C-C bonds and one new C_aryl -O bond through both intramolecular and intermolecular reactions. The reaction is easy to perform, proceeds under mild conditions, and exhibits excellent regioselectivity. Water, a simple and readily available reagent, was employed as the OH source. A plausible reaction mechanism is proposed for this new annulation based on isotopic substitution experiments.

A practical synthesis of chiral tricyclic cyclopenta[b]benzofuran, a key intermediate of Beraprost

A novel formal synthesis of Beraprost (1) is described.

endo/exo stereoselectivity in Diels-Alder reactions of α,β-dialkylated conjugated enals to cyclic 1,3-dienes: intermediates in the synthesis of (-)-β-santalol and its analogs

Highly exo-selective [4+2] cycloadditions of cyclopenta-1,3-diene 2a to α,β-dialkyl conjugated enals 5 are compared with the analogous endo-favored Diels-Alder reaction of cyclohexa-1,3-diene 7. The exo-stereoselectivity is lower in the homologous case of methylcyclopenta-1,3-diene 9. This diastereoselectivity is discussed either in terms of a retro-homo-Diels-Alder reaction, associated with thermodynamic control, or with respect to either a competing hetero-Diels-Alder/Claisen or Cope domino pathway, or retro-Claisen/retro-hetero-Diels-Alder of the endo-homo-cycloadducts. These hypothetical mechanisms have been examined by DFT calculations at the MPW1K(CH2 Cl2 )/6-31+G** level of theory for the AlCl3 -mediated cycloadditions of 5d to 2a and 7. Application of Corey's methodology to the γ-halogeno-α-methyl-substituted dienophiles 5a and 5b allowed an enantioselective preparation of known and useful intermediates for the synthesis of either the naturally occurring (-)-β-santalol or its potentially olfactive structural analogs.

Stereoselective amination of chiral benzylic ethers using chlorosulfonyl isocyanate: total synthesis of (+)-sertraline

The stereoselective amination of various chiral benzylic ethers using chlorosulfonyl isocyanate is developed, and the application of this method to the total synthesis of a potent antidepressant, (+)-sertraline, from readily available 1-naphthol is also described.