Intramolecular Diels−Alder Reactions of Optically Active Allenic Ketones: Chirality Transfer in the Preparation of Substituted Oxa-Bridged Octalones

The intramolecular Diels-Alder reaction of allenic ketones containing a furyl unit (IMDAF) to generate oxatricyclic systems in good yields is described. The alkene dienophiles 1ab give poor yields of the cycloadducts 2ab, presumably due to the facile retro Diels-Alder reaction. However, the analogous allenic dienophile 7 afforded the desired cycloadduct 8 in 91% yield on treatment with dimethylaluminum chloride. When the allene bears an alkyl substituent on the terminal carbon, complete diastereoselectivity is seen in the IMDAF, e.g. cyclization of 14 gave only the cycloadduct 15 in 80% yield presumably due to greater steric hindrance in the transition state II as compared to that in I. Finally we report complete chirality transfer of the stereochemistry of an allene to the carbon framework of the oxatricyclic system. Thus, the optically active allenic ketone 20 afforded only the desired cycloadduct 21 with the correct absolute stereochemistry needed for the synthesis of the arisugacin class of natural products.

Novel synthetic analogs of the Pseudomonas autoinducer

Release of virulence factors in Pseudomonas aeruginosa is regulated by two N-acylhomoserine lactones, PAI-1 and PAI-2, that activate the respective transcription factors LasR and RhlR. With the goal of developing novel therapeutic agents, we synthesized constrained analogs of PAI-1 and evaluated them in P. aeruginosa. Two of the novel analogs bound to LasR and showed agonist activity in LasR stimulation of a lasI-lacZ reporter construct.

Why Do Catalytic Quantities of Lewis Acid Generally Yield More Product than 1.1 Equiv in the Intramolecular Diels-Alder Reaction with a Furan Diene? 2.(1) AM1 Calculations and Mathematical Simulation of the Equilibria

The results presented here provide additional support for our hypothesis based on the relative basicity of the reaction controlling functional group to rationalize experimental observations on intramolecular Diels-Alder reactions with a furan diene (IMDAF) regarding the quantity (0.1 or 1.1 equiv) of Lewis acid required to facilitate the reaction most effectively. Heats of formation, DeltaH(f), and heats of reaction, DeltaH(R), have been obtained using AM1 calculations for 26 IMDAF reactions. These DeltaH(R) are generally exothermic (indicating that these IMDAF reactions are favorable) and can be qualitatively correlated with experimental yields of adduct, thereby providing a means of predicting the feasibility of the IMDAF promoted by 0.1 equiv of Lewis acid. The equilibria involved in the Lewis acid-promoted IMDAF reaction have been qualitatively interpreted using reaction coordinate diagrams and quantitatively investigated by generating a mathematical simulation of the reaction scheme. This demonstrates that the experimental behavior of the IMDAF reaction is well represented by the relative basicity hypothesis and that the LA concentration-dependent behavior should also be observed for other Lewis acid-promoted organic reactions.