| Summary: | Chapter 1 briefly covers the development and utility of allylboron reagents in organic synthesis. Transition models proposed for addition to carbonyl groups and imines are discussed and selected examples of the utility of these reagents to the synthesis of complex molecule covered.
In chapter 2 the allylation and crotylation of ketones using allyl- and crotyltrifluoroborates and montmorillonite K-10 are described. The method is scalable and utilizes a reliable catalyst with high functional group tolerance. A conventional work-up is not required for further purification, since the boric acid by-product of the reagent remains trapped in the cavity of the K-10. The method is quite robust and provides an operationally straightforward procedure for the allylation of a range of ketones using the air and moisture stable potassium allyltrifluoroborate.
In Chapter 3, the first indium-mediated highly chemo- and diastereoselective allylation of α,β-
epoxyketones using allyltrifluoroborate was developed. It was shown in the case of simple ketone substrates, the loading of indium can be reduced to catalytic quantities without a diminishment in yield. The stereochemical nature of the epoxy homoallylic alcohols was
ii
unequivocally established through Payne rearrangement. Mechanistic studies indicate that the reaction proceeds through an allylindium species; although the nature of the indium species was not fully elucidated.
Finally, in chapter 4 regioselective allylation and diastereoselective crotylation of various indoles are discussed using BF3·Et2O as a promoter. It was shown that the electronic effects of the substituents on the indole ring had little effect on the outcome of the reaction. However, steric factors were more influential on the yields and reactivity of the substrates. Stereospecific addition of the E- and Z-crotyltrifluoroborates could also be achieved under the reaction conditions, providing the corresponding anti and syn products, respectively.
|
|---|
