Ring-Opening Reactions Of Cyclopropenes With Organometallic Reagents

Cyclopropene is the smallest carbocycle containing a C-C double bond. There have been many reports on transformations of the C=C bond of cyclopropenes, including hydrogenation, cross-coupling reaction, and also the addition of organometallic reagents to the C-C double bond affording multi-substituted cyclopropanes. On the other hand, the highly strained structures make them easy to undergo C-C bond cleavage reaction leading to a series of unsaturated compounds. This dissertation mainly investigated the ring-opening reactions of cyclopropene derivatives with organometallic reagents affording a series of multi-substituted alkenes and benzocycles efficiently.The ring-opening reactions of cyclopropenes with Grignard reagents were studied firstly. Existing reports on their reactions mainly focused on the carbometallation of the C-C double bonds of cyclopropenes. Our study showed that highly regio-and stereoselective ring-opening reactions occurred between cyclopropenes with two electron-withdrawing groups and Grignard reagents. It should be noted that the ester group didn’t react with the Grignard reagents. Both alkyl and phenyl Grignard reagents are compatible, generating a series of multi-substituted not-readily-available alkenyl malonate derivatives efficiently. Beside H+, other electrophiles such as allyllic halides, iodine and propargyl bromide could be introduced to yield dienes, alkenyl iodides and alkenyl allenes. With careful mechanistic study, a dimagnesium intermediate was identified. This is the first ring-opening reaction of cyclopropene derivatives with Grignard reagents.Further studies showed that organozinc and organolithium reagents could both promote the ring-opening reactions of cyclopropenes giving similar results to Grignard reagents. While organoaluminum reagents could react with cyclopropenes without catalyst in proper solvents such as hexane and dicholomethane, generating ring-opening products with a reversed regioselectivity.The nucleophilic ring-opening process was further extended to intramolecular reactions:by addition of organolithium reagents, deprotonation-cyclization -ring-opening reactions of (2-acetoxyphenyl)cyclopropene derivatives occurred highly selectively, generating a series of useful benzofuran derivatives in good yields.The last part of the dissertation was developed based on our previously developed oxidation of allenyl alcohols catalyzed by copper chloride and1:1ratio of1,10-phenanthroline and2.2’-bipyridine. We further applied the system to the aerobic oxidation of allylie and propargylic alcohols to prepare a series of α,β-unsaturated carbonyl compounds.