Part I. One-Pot Reductive Allylation of α-Fluorinated Esters Part II. Investigation of Magnetic Field Effects on the Organic Reactions via Biradical Intermediates

Abstract

Part I. Fluorine-containing homoallylic alcohols are useful synthetic precursors because of their abundant reactive sites that can be transformed into other functional groups. Among various types of fluorinated homoallylic alcohols, β’-fluorinated homoallylic alcohols can be prepared by allylation of fluorinated ketones and aldehydes. However, fluorinated aldehydes are hard to handle because of their poor stability, thereby necessitating the development of another practical strategy for the synthesis of the β’-fluorinated homoallylic alcohols. Traditionally, one-pot reductive transformations of esters were considered a suitable solution that avoided the isolation of unstable aldehyde intermediates. On the basis of this strategy, it was envisioned that one-pot reductive allylation of fluorinated esters would also be practically advantageous to the preparation of β’-fluorinated homoallylic alcohols. In part I, the preliminary efforts to accomplish the one-pot reductive allylation of fluorinated esters are presented. Several control experiments suggested both high temperature and water are necessary because the tetrahedron intermediate generated by DIBAL reduction is unreactive at the low temperature even in the presence of allylBpin. In addition, water serves as both quencher of the reducing agent and trapper of the unstable fluorinated aldehyde, preventing the over-reduction. As a result, the desired product yield was improved to 68%. Part II. Beyond the traditional thermal energy, there have been much efforts to employ other driving forces for organic reactions, and these endeavors brought the remarkable development of photochemistry, electrochemistry, and mechanochemistry. On the contrary, utilizations of the magnetic force in organic synthesis are far less developed. Only few studies regarding the magnetic fields effects (MFE) for organic reactions were reported, but most of them were inefficient, irreproducible, or even manipulated. On the other hand, in the physical chemistry area, magnetic fields are employed to prevent the intersystem crossing of biradical species. On the basis of these principles, it was expected that magnetic field could affect the spin state population of biradical species to result in the alternation of the efficiency on radical recombination reactions. In this part, we investigated the MFE on four types of biradical-mediated organic reactions: spin-directed Paternò-Büchi reaction of propionaldehyde and 2,3-dihydrofuran, nitrogen deletion reaction of secondary amines, photochemical cyclization of 2-allyloxybenzophenone, and rearrangement of vinylated chrysanthenone. Unfortunately, no noticeable MFE was observed.