Annual Research Report, 1996

The research objective of this research group is the development of novel reactions that will generate novel strategies for formation and cleavage of chemical bonds connected to a carbon atom. To this end, we are studying the behavior of molecules of complex electronic and structural properties such as open shell reactive intermediates, polyatomic compounds and chemical environments where reactions take place.

(1) Design and synthesis of functional molecules bearing fullerene as core structure

(2) Olefin carbometalation reactions

(1) Design and synthesis of functional molecules bearing fullerene as core structure

We have discovered a remarkable reaction, with which five phenyl groups can be introduced to [60]fullerene in quantitative yield. This penta addition of phenyl group isolate a single pentagon in the fullerene as cyclopent-adienyl anion, which forms 6p-electron metal complexes with various metals. The transformation can be readily achieved by treatment of the fullerene with excess Ph2Cu-, generating C60Ph5H after water quenching. Such a cyclopentadienyl ligand will prove to be useful for design of metal catalysts that responds to outside stimuli.

With the aid of carbene chemistry previously developed in these laboratories, we have regio- and stereospecifically functionalized two of 30 double bond on [60]fullerene. Among several compounds thus synthesized, the C2 symmetric fullerene shown below is particularly unique since its preparation marked the first asymmetric synthesis of optically active doubly functionalized fullerene. With such methodologies, we have elucidated various bioactivities of water soluble fullerenes including cytotoxicity, DNA cleaving activity and AIDS protease inhibitory activity.

A-6) J. Am. Chem. Soc. 118, 12850-12851 (1996)

A-1) J. Chem. Soc., Chem. Commun. 1747-1748 (1996)

A-2) Bull. Soc. Chem. Jpn. 69, 2143-2151 (1996)

(2) Olefin carbometalation reactions

By the use of the optically active zinc reagent shown, we have previously achieved the first asymmetric carbometalation of simple olefins. The reagent has now been shown to achieve highly enantioselective carbometalation of imines, which opened up a new route to optically active amines.

Side by side with experimental work, we are carrying out large-scale quantum mechanical calculations, and have studied the behavior of aggregated organometallics. Such species are well recognized as true reactive species in solution, but their behavior has not been well understood at molecular levels.D

A-7) J. Am. Chem. Soc. 18, 8489-8490 (1996)

A-12) J. Org. Chem. 62, 792-793 (1997)