Studies On The Synthesis And Electrophilic Reactions Of Allenols

In this dissertation, much attention has been focused on the synthesis of 2,3-allenols and its electrophilic 1,2-shift reactions with X+. The whole dissertation can be divided into three parts:PartⅠ:Electrophilic 1,2-shift reactions of 2,3-allenols with electrophilic halogen atom reagentsFirstly, we studied the electrophilic 1,2-shift reactions of secondary 2,3-allenols with X+. It was found that different substitutent groups have different tendancy for 1,2-shift:When there is an aryl group at the a-position, the reaction affordedβ-halo-β,γ-alkenals via a 1,2-aryl shift; when there is a methyl group on the a-position, the reaction affordedβ-halo-β,γ-alkenones via a 1,2-H shift.Secondly, we studied the electrophilic 1,2-shift reactions of tertiary 2,3-allenols with NBS. It was found that solvent effect have a great impact on the reaction selectivity. Water was found to be the best solvent, which affordedβ-bromo-β,γ-alkenones with high regioselectivity. When the a-substitutent groups are both alkyl groups, the reaction proceeded via a 1,2-alkyl shift; with cyclic allenols, a ring expansion was observed to affordα-(1'-bromo)vinylcyclic ketones. When there's at least one aryl group at theα-position, the reaction proceeded via a 1,2-aryl shift. Based on the above results, we have also developed an effective method for the synthesis of 1,2-allenic ketones from tertiary 2,3-allenols.PartⅡ:Preparation of optically active 2,3-allenolsWe have developed an effective methodology for the CuBr-catalyzed one-pot synthesis of simple allenes from terminal alkynes. Based on this work, we synthesized optically active secondary 2,3-allenols from racemic propargyl alcohols with up to 99.7% ee value in three steps.However, the yield is not satisfactory and only optically active 1-aryl-2,3-allenols can be prepared.In order to solve these problems, we developed the CuCN-catalyzed carbometallation of optically active 4-chloro-2-butynols with alkyl Grignard reagent, which afforded optically active secondary 2,3-allenols with good yield and up to 99.9% ee value. Compared with the above CuBr-catalyzed synthesis of 2,3-allenols, the yield is satisfactory and the 1-substituent group can be aryl or alkyl group. When aryl Grignard reagents reacted with 4-chloro-2-butynols, the reaction afforded propargyl alcohols instead of 2,3-allenols.PartⅢ:Electrophilic 1,2-shift reactions of optically active 2,3-allenols with bromineAfter being successful in the synthesis of optically active 2,3-allenols with high ee value, we studied the electrophilic reaction of optically active 2,3-allenols with bromine and demonstrated that this reaction afforded optically activeβ-bromo-β,γ-alkenals with high regioselectivity. The chirality of the optically active 2,3-allenols can be partly transferred into the center chirality in the final products with up to 76.0% ee value.