Studies On Electrophilic Cyciization Of Propargyl Alcohols

This thesis mainly aims at the studies on the electrophilic cyclization of propargyl alcohol derivatives, which chiefly involves the following five chapters.Chapter I:In chapter I, development and application of useful and important reactions of propargyl alcohols in organic synthesis were summarized in detail. Propargyl alcohols were known as important difunctionalized intermediates in organic reactions. Because of the role of mutual activation between alkynyl group and hydroxyl group, this kind of substrate showed a unique and diverse reactivity. Based on this point, we facilitated a detailed description of six different reactions.(1) Bronsted acid or transition-metal catalyzed Meyer-Schuster rearrangement reaction;(2) transition-metal or Bronsted base catalyzed isomerization reaction;(3) transition-metal catalyzed propargyl substitution reaction;(4) transition-metal or Bronsted acid catalyzed tandem cyclization reaction;(5) transition-metal catalyzed cross-coupling reaction;(6) electrophile-promoted tandem cyclization reaction.Chapter II:In chapter II, we first introduced our group’s works on the eletrophilic cyclization of propargyl alcohols. Based on these research achievements, we developed a concise method for the synthesis of diiodinated indenes, dihydronaphthalenes and dihydrobenzo[b]oxepines from simple aryl propargyl alcohols via an iodocyclization. The resulting diiodide could be further exploited by Pd-catalyzed coupling reaction. Noteworthily, when the amount of substrate was increased to one gram, the desired product was also obtained in moderate yield. By compared experiments, the presence of a trace amount of water was essential for this electrophilic cyclization.Chapter Ⅲ:In chapter Ⅲ, the traditional methods for the synthesis of furan-2-one derivatives were briefly summarized. Next, we described in detail an efficient approach to highly regioselective synthesis of dihalogenated furan-2-ones from4-hydroxy-2-alkynoates. Using IC1, IBr and I2as electrophiles, we generated the desired products bearing different halogen substituents. Moreover, the resulting halides could further afford polycyclic aromatic compounds using known palladium-catalyzed coupling reactions. Interestingly, we employed different coupling conditions to smoothly obtain mono-or disubstituted products.Chapter IV:In chapter IV, a novel spirocyclization of propargyl alcohols induced by iodine molecular has been developed. In this reaction, it was believed that the allene cation intermediate could be captured by the oxygen of the carbonyl group instead of the iodine anion. This sequential cascade process was concisely conducted at room temperature. A variety of propargyl alcohol substrates underwent this iodocyclization, giving the desired spiro-products in good yields. The reaction of substrates with different substituents on the aryl group showed certain chemistry selectivity.Chapter V:In chapter V, the developments for synthesis of spiroketal compounds were briefly summed up and then an efficient synthetic approach to tetrahalogenated spiroketals was elaborated through a tandem iodocyclization of various a,β-diynyl keto diols. This iodocyclization accommodated a wide range of functional groups and proceeded under mild conditions. To further explore the mechanism of this electrophilic spiroketalization, the reactions of chiral a,β-diynyl keto diol derivatives with I2were examined under similar conditions. The experiment results indicated that the chiral spiroketal center was induced by chiral alcohols and this spiroketalization was achieved through a cooperative process.