1,4-Dipole forming photoreactions of alpha-trimethylsilyl and alpha-tributylstannyl substituted alpha-ketoamides, and, Mechanistic studies of photomacrocyclization reactions and their application in crown ether synthesis and fluorescence sensing of metal cations.

摘要

In the early photochemical studies of alpha-ketoamides leading to beta-lactams formation, two mechanisms were proposed for this process. One, suggested by Aoyama, involves excited-state H-atom abstraction while the other, put forth by Whitten, follows a sequential SET-proton-transfer route. The photochemical properties of N-trimethylsilylmethyl- and N-tributylstannylmethyl-substituted alpha-ketoamides were explored in order to gain information about the mechanism of this process and to develop a regioselective method for beta-lactam formation. The results of this effort show that (1) photoreactions of N-trimethylsilylmethyl-substituted alpha-ketoamides proceed by competitive H-atom abstraction and sequential SET-desilylation pathways and (2) a sequential SET-destannylation pathway is preferentially followed in photochemical reactions of the tributylstannylmethyl-substituted alpha-ketoamides. Expansion of this SET-destannylation induced 1,4-dipole formation chemistry including (1) trapping of the 1,4-dipole intermediates, (2) application of this synthesis useful chemistry in synthesizing biologically active compounds and (3) photochemistry of alpha-iminoamides were studied.; The physical and chemical properties of crown ethers have been investigated for many years. However, the approaches for synthesizing crown ethers are still in demand. In this effort, photomacrocyclization reactions of trimethylsilyl terminated, polyether tethered naphthalimides are used to construct the crown ether macrocyclic ring. Acylation of the resulting amidols followed by extension of the side chain gives the lariat type crown ethers. Measurement of cation extraction constants and investigation of fluorescence properties of these substrates show that (1) these substrates are better cation complexor than 18-crown-6 and aza-18-crown-6 and (2) Mg2+, Cu 2+ and Ag+ but not alkali metal cations affect the fluorescence intensities of these substrates indicating an "off-on" sensing effect. Moreover, studies of "electron hopping effect" of these substrates and their counterparts show that the relative quantum yields of photoreactions of these substrates are dependent on their ether chain length and numbers of oxygen in the chain.