Reaction Studies On The Reactivity Of Propargylic Esters And Aziridines

This dissertation mainly focused on the reactions of propargylic esters and aziridines. Propargylic esters have highly valuable reactivity to undergo1,2-or1,3-acyloxy migration in the presence of gold or silver catalyst, leading to the formation of a metal-carbene or an allenic intermediate. In the presence of metal Lewis acid (TiCl4,BiCl3et al), the acyloxy group can undergo leaving to afford carbocation intermediate. These active intermediates can further transform to valuable molecules. Functionalized aziridines have shown a broad utility in organic chemistry due to their highly strained ring and the presence of the particular substitution which feature noticeable unique reactivities. Enlightened by these, we developed series of methodologies for building a variety of heterocyclic compounds and nitrogen-containing compounds. The dissertation can be divided into two parts:Part I:The Cyclization of Propargylic EstersWe have reported a novel TiCl4-mediated carbocyclization of1,6-enynes containing propargylic ester moiety. By controlling the reaction temperature,3-azabicyclo[3.1.0]hexanes and functionalized allenes could be synthesized respectively in moderate to good yields along with moderate to high diastereoselectivities (Chapter1.1).Titanium(IV) chloride-mediated intramolecular ring enlargement of methylenecyclopropanes with propargylic esters has been explored, affording the corresponding chlorinated bicyclo[4.2.0]oct-5-ene derivatives in moderate to good yields under mild conditions. The E-and Z-methylenecyclopropanes could all be converted to the corresponding cis-bicyclo[4.2.0]oct-5-enes with moderate to high diastereoselectivities (Chapter1.2).We have developed a silver-catalyzed intramolecular transformation of propargylic esters with N-sulfonylhydrazones to give5,6-dihydropyridazin-4-one derivatives in moderate to good yields under mild conditions. This novel reaction procedure involved a tandem1,3-acyloxy migration/Mannich-type addition/elimination of sulfonyl group sequence. In addition, the corresponding products could be easily converted to5-hydroxypyridazin-4-ones and1,6-dihydropyridazins (Chapter2).Part II:The Ring-openging Reaction of AziridinesA novel gold(I)-catalyzed domino transformation of aziridinyl alkynes with arenes to construct1.2.3.4-tetrahydroisoquinoline as well as3,4-dihydroisoquinoline structural motifs, especially sterically congested syn-3,4-disubstituted1,2,3,4-tetrahydroisoquinolines, has been described. A plausible mechanism proceeding with a benzylic cation has been given on the basis of deuterium-labeling and control experiments as well as the observed diastereoselectivities (Chapter3).We have developed a novel Lewis acid-catalysed ring-opening reaction of N-(aziridin-2-ylmethylene)hydrazines to construct enamine derivatives in good yields under mild conditions. An anchimeric assistance of the anchored hydrazone moiety in the ring-opening of N-(aziridin-2-ylmethylene)hydrazines and a1.2-migration is proposed (Chapter4.1).We prepared N-(aziridin-2-ylethylidene)hydrazines and N-(aziridin-2-ylbutylidene)hydr-azines from ketons derived hydrazines and submitted them to Lewis acid and TfOH. We found no enamines but2-pyrazolines and a,(3-diamino ketones. The aziridines undergo ring-opening through a SN2-type pathway and the electronic effects of the substrates govern the reactivity and thus the ring-opening process. Nonracemic2-pyrazolines and α,β-diamino ketone could be obtainted from chiral aziridines (Chapter4.2).Part III:Gold-Catalyzed Cyclization of1-(Indol-3-yl)-3-alkyn-1-olsAn efficient cyclization of1-(indol-3-yl)-3-alkyn-l-ols in the presence of cationic gold(I) complex leading to annulated or specific substituted carbazoles was observed. Depending on the reaction conditions and the substitution pattern, divergent reaction pathways were discovered furnishing diversified structures:cycloalkyl-annulated[b]carbazoles are obtained via1,2-alkyl migration of the metal-carbene intermediates; cycloalkyl-annulated[af]carbazoles are formed via a Wagner-Meerwein type1,2-alkyl shift and carbazole ethers are formed through ring-opening of cyclopropyl group by nucleophilic attack of water or alcohol.