Rickborn

To resolve this problem, Rickborn made an ingenious proposal that implicated the intermediacy of a bimetallic transition structure assembly v involving a bridging Znl2 molecule (Fig. 3.5). This would accommodate the needed spatial requirements of the methylene transfer process. The importance of the polymetallic re-... 

Understanding the importance of the zinc alkoxide, the iodomethylzinc iodide and the zinc sulfonamide allowed Denmark to propose a revised transition state structure xv (Fig. 3.22) [82]. In this picture, the complex, polymetallic aggregate invoked by Rickborn and later by Kobayashi is featured. 

F. R. Jenson and B. Rickborn, Electrophilic Substitution in Organomercurials, McGraw Hill, New York, 1968. 

The first evidence of an anionic Diels Alder reaction was given by Rickborn [25a]. The reaction of anthrone with N-methylmaleimide in CHCI3 or THE occurs with low yield [26] (Equation 1.10), while in DMF or in the presence of catalytic amounts of amine (EtsN, Py) the reaction is completed in a few minutes [25]. 

Rickborn B. The Retro-Diels-Alder Reaction. Part II. Dienoplules with One or More Heteroatoms Org. React. (N. Y.) 1998 53 223-629... 

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