Investigation of Ring-Openings of Some gem-Dichlorocyclopropanes

Abstract

The main purpose of this thesis was to study ring-openings of gem-dichlorocyclopropanes under basic conditions and the formation of acetylenic acetals. Therefore, several 2-alkoxy-1,1-dichlorocyclopropanes were synthesized by addition of dichlorocarbene to the corresponding vinyl ethers under phase-transfer conditions or by Doering Hoffmann conditions. These 2-alkoxy-1,1-dichlorocyclopropanes were treated with 4 eq. of NaOCH3 in DMF at -10°C for 4 hours and quenched with water at room temperature. This gave the optimal yield of acetylenic acetals. However, a slightly different condition was approached for cyclopropanes of cyclic compounds like 7,7-dichloro-2-oxabicyclo[4.1.0]heptane (41), 1-methoxy-7,7-dichlorobicyclo[6.1.0]nonane (42) and 13,13-dichloro-1-methoxybicyclo[10.1.0]tridecane (43). They were treated with sodium methoxide in DMF at 0°C for the highest yield of their corresponding products (54), (3,3-dimethoxy)cyclononyne (55), and (3,3-dimethoxy)cyclotridecyne (56). It is believed that the formation of acetylenic acetals most likely involves a cyclopropene as an intermediate, which might also rearrange to the corresponding vinyl carbene and later form an adduct with alkenes. Therefore, trapping experiments using several non-nucleophilic bases were performed which resulted in the formation of such adducts. In this master thesis, several compounds were synthesized for the formation of acetylenic acetals. To the authors best knowledge, compounds (16), (17), (30), (37), (38), (39), (40), (43), (49), (50), (51), (52), (53), (55) and (56) have not been prepared before. (see Appendix A)