Intramolecular Diels-Alder Reactions of Decatrienoates: Remote Stereocontrol and Conformational Activation(1).

The intramolecular Diels-Alder (IMDA) reactions of C(8)-substituted decatrienoates have been studied. The stereospecific formation of 11 via an endo-boat-9 transition state attests to the powerful directing influence of a C(8) substituent in the IMDA of decatrienoate. In addition, the contrasting observations that stereospecific 9 --> 11 occurs at room temperature while the nor-tert-butyl substrate (4a) requires 125 degrees C/5 h reaction conditions and produces a 60:40 mixture of diastereomers provide clear evidence that a bulky C(8) substituent is a powerful conformational activator of the IMDA.

Sequential 1,3-dipolar cycloadditions in the synthesis of bis-isoxazolo substituted piperidinones

A strategy for the efficient synthesis of novel bis-isoxazolo substituted piperidinones has been developed. The protocol consists of the Michael addition of an unsaturated alkoxide to beta-nitrostyrene followed by an intramolecular nitrile oxide cycloaddition (INOC) or an intramolecular silyl nitronate olefin cycloaddition (ISOC) to give III. Grignard addition to this isoxazoline intermediate followed by DCC coupling of the resulting isoxazolidine with nitroacetic acid gave II, and a second intramolecular cycloaddition via 1,3-dipoles result in the formation of the targeted novel tetracycles (I). A solid-supported scavenger was employed to increase the efficiency and yield of the Michael addition step.

Tetrapyrroles as pi Donors: A Pd(2)(2+) Unit Sandwiched between Two Helical Bilindione-Palladium Moieties.

Metalation of octaethylbilindione (H(3)OEB) with palladium(II) acetate produces the novel tetranuclear complex [Pd(4)(OEB)(2)] in which a (Pd(I)(2))(2+) unit is sandwiched between two helical Pd(OEB) units (see picture). Treatment of [Pd(4)(OEB)(2)] with pyridine/ethanol gives the odd-electron helical complex [Pd(OEB)].