Asymmetric Allylic Alkylation Of MBH Carbonates And Allyl Ketones And Synthetic Studies Of C₂-symmetric Guanidines

In recent years, organocatalysis has received great attention in asymmetric synthesis for its enzymemimic, metal-free, atomatically economic and low toxic characters. Organocatalytic reactions are becomingpowerful tools in the construction of complex molecular skeletons.At the same time, the metal-free organic Lewis base-catalysed allylic alkylation ofMorita–Baylis–Hillman （MBH） adducts has recently emerged as a powerful strategy to producemultifunctional allylic-substituted compounds, in which exclusive regioselectivity has been generally noted.Moreover, two novel C₂-symmetric chiral guanidine organocatalysts have been synthesized. Thedissertation includes five topics as below shown:1. Asymmetric allylic alkylation of Morita-Baylis-Hillman （MBH） carbonates with allyl ketonesThe asymmetric allylic alkylation of Morita-Baylis-Hillman （MBH） carbonates with allyl ketones hasbeen developed. The α-regioselective alkylation adducts, containing a hexa-1,5-diene framework withimportant synthetic value, were achieved in up to83%yield,>99%ee and50:1dr by using a commerciallyavailable Cinchona alkaloid as the catalyst. From the allylic alkylation adduct, cyclohexenes bearing twoadjacent chiral centers were readily obtained. 2. Design and synthesis of novel C₂-symmetric chiral guanidine organocatalystsTwo new C₂-symmetric chiral guanidines as small molecule organocatalysts have been designed andsynthesized. According to the retrosynthetic analyses, two novel strategies have been developed. Bicyclicguanidine obtained from L-methionine and L-asparagine, through9steps, in12.4%overall yield, withaverage79%yield of each step. Guanidine precursor based on spiro skeletoncould be obtained from simple,cheap commercially available m-bromo anisole, through10steps, in10.1%overall yield, with average80%yield of each step.