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Chlorins bearing synthetic handles at specific sites about the perimeter of the macrocycle constitute valuable building blocks. We previously developed methodology for preparing meso-substituted chlorin building blocks and now present methodology for preparing several complementary beta-substituted chlorin building blocks. The chlorins bear one or two beta substituents, one meso substituent, a geminal dimethyl group to lock in the chlorin hydrogenation level, and no flanking meso and beta substituents. The synthesis involves convergent joining of an Eastern half and a Western half. New routes have been developed to two beta-substituted bromo-dipyrromethane monocarbinols (Eastern halves). A new beta-substituted Western half was prepared following the method for preparing an unsubstituted Western half (3,3-dimethyl-2,3-dihydrodipyrrin). Chlorin formation is achieved by a two-flask process of acid-catalyzed condensation followed by metal-mediated oxidative cyclization. beta-Substituted chlorins have been prepared in 18-24% yield bearing a 4-iodophenyl group at the 8-position, a 4-iodophenyl group or a 4-[2-(trimethylsilyl)ethynyl]phenyl group at the 12-position, and a 4-iodophenyl group and a 4-[2-(trimethylsilyl)ethynyl]phenyl group at diametrically opposed beta-positions (2, 12). The latter building block makes possible the stepwise construction of linear multi-chlorin architectures. The chlorins exhibit typical absorption and fluorescence spectra. A systematic shift in the absorption maximum (637-655 nm for the free base chlorins, 606-628 nm for the zinc chlorins) and intensity of the chlorin Q(y)() band (epsilon up to 79 000 M(-)(1) cm(-)(1)) is observed depending on the location of the substituents. The characteristic spectral features and location of substituents in defined positions make these chlorins well suited for a variety of applications in biomimetic and materials chemistry.

This lecture describes some of our studies of lithio derivatives of allyl sulfone car- banions which add α -regioselectively as well as anti diastereoselectively to Michael accep- tor olefins. This can be ascribed to chelation in the Michael addition step. When the reaction leads to subsequent ring closure by using a bromoallyl sulfone, the latter acts as a methylen- emethane synthon in a (3+2) Michael-initiated ring closure, affording highly functionalized cyclopentane derivatives Such additions proceed with high stereoselectivity and with asym- metric induction leading to nonracemic substituted cyclopentanones. Additions of allyl sul- fone carbanions also proceed stereoselectively to C=N systems containing a chiral auxiliary on N. These can be used in the synthesis of optically active five- and six-membered ring N- heterocycles. Furthermore, chiral groups on the allyl sulfone moiety can induce significant remote asymmetric induction, made possible by the presence of an aromatic π-system which promotes intramolecular chelation to the Li cation.