Efficient Microwave Assisted Syntheses of 2,5-Diketopiperazines in Aqueous Media

Aqueous in situ one-pot N-Boc-deprotection-cyclization of Nα-Boc-dipeptidyl-tert-butyl and methyl esters under microwave irradiation afforded 2,5-diketopiperazines (DKPs) in excellent yields. This protocol is rapid, safe, environmentally friendly, and highly efficient, and showed that the tert-butoxy moiety is also an excellent leaving group for these cyclizations

Oxazolidine-2-thiones and Thiazolidine-2-thiones as Nucleophiles in Intermolecular Michael Additions

Conjugate addition of thiazolidinethiones and oxazolidinethiones to <i>N</i>-crotonylthiazolidinethiones and -oxazolidinethiones was observed in the presence of excess triethylamine in dichloromethane. The addition takes place by the nitrogen of the heterocycle with high diastereoselectivity. It was observed that the stereoselective addition occurs on the <i>anti</i>-s<i>-cis</i> conformation of the <i>N</i>-enoyl sulfur-containing heterocycle

Karwinaphthopyranones from the Fruits of <i>Karwinskia parvifolia</i> and Their Cytotoxic Activities

The new 2-acetyl-8-methoxynaphthol (<b>1</b>) and five new “dimeric” napthopyranones, karwinaphthopyranones A1 and A2 (<b>2</b> and <b>3</b>) and karwinaphthopyranones B1–B3 (<b>4</b>–<b>6</b>), possessing a methoxy group at C-5′, were isolated together with four other known compounds from the dried fruits of <i>Karwinskia parvifolia</i>. The structures of compounds <b>2</b>–<b>6</b> were determined by spectroscopic data interpretation. Cell culture assays showed that some of these compounds possess antiproliferative activities in representative human cancer cell lines, with half-maximal growth inhibitory concentrations in the micromolar range

Chemoselective Reduction of Trichloromethyl Compounds to <i>gem</i>-Dichloromethyl Groups Following Appel’s Reaction Protocol

A simple and easy reduction of trichloroacetyl compounds following the modification of Appel’s reaction protocol, using triphenylphosphine and methanol, afforded the corresponding dichloroacetyl compounds, with the exception of trichloro­acetyl­morpholine, in yields of 80–98% under very mild experimental conditions. Likewise, when trichloromethyl heterocyclic compounds contain another reactive functional group, the reaction is highly chemoselective giving the dichloromethyl derivative

Chemoselective Aromatic C–H Insertion of α-Diazo-β-ketoesters Catalyzed by Dirhodium(II) Carboxylates

The ability of α-diazo-β-ketoesters bearing a substituent on the benzylic position to undergo aromatic C–H insertion is described. Good to excellent yields of the aromatic C–H insertion products were observed with Rh₂(tpa)₄ or Rh₂(esp)₂ catalysts. This is an attractive strategy to prepare tetralins carrying a methyl group on the benzylic position, a structural motif found in several types of natural products