| Much progress has been made on the selective electrophilic and nucleophilic addition of allenes in our group. Based on these previous studies, the attention of my doctoral dissertation has been focused on the the electro-and nucleophilic addition reactions of functionalized allenes with high selectivity.1) The iodohydroxylation of1,2-allenyl sulfoxides with iodine in the presence of benzyl thiol afforded3-hydroxy-2-iodo-2(E)-alkenyl sulfides in good yields and high regio-and stereoselectivities. In this reaction, it was observed that the sulfoxide functionality was reduced to sulfide and the water in the reaction mixture plays an important role for the stereoselectiviry observed.2) Based on the study of iodohydroxylation of1,2-allenyl sulfoxides with iodine in the presence of benzyl thiol, we found that a-iodo-α,β-unsaturated ketones or aldehydes were formed when the reaction was conducted at a higher temperature (40℃). In this reaction, hydrogen bonding may mediate an efficient and highly selective cleavage of the O=S bond and C-S bond in1,2-allenyl sulfoxides with I2and BnSH, which transfer the oxygen to the adjacent allenylic carbon atom forming the ketone or aldehyde carbonyl functionality with one C=C bond in the allene moiety remained in a highly stereoselective manner.3) The reaction of diaryl-2,3-allenyl ethers with NBS in the mixed solvents (CH3NO2/EtOH) affords highly functionalized2-bromonaphthalenes or2-bromophenanthrenes. According to the studies on the effects of solvent, temperature, concentration, and loading of NBS on the reaction, a set of optimized conditions has been identified to explore the scope of the reaction forming2-bromonaphthalenes and2-bromophenanthrenes in good yields. The electronic effect on the aryl is important to the selectivity of the reaction. Different electron-donating groups and electron-withdrawing groups were also explored.4) Dr. Zhao Fang in this group developed the reaction of2,3-allenoates with aromatic aldehydes, and studied the scope of the reaction. Based on these, the mechanism of the reaction was studied. Isolation of3,4-diaryloxetanes intermediate led to a rationale involving1,2-addition and an intramolecular nucleophilic addition of allenoates for this reaction. After studying the effects of solvent, base, and catalyst, the optimized conditions affording cis-3,4-diaryloxetanes have been identified and the scope was also investigated. |
