First Highly Regio- and Diastereoselective [3+2] Cycloaddition of Chiral Nonracemic Alkenyl Fischer Carbene Complexes with Diazomethane Derivatives: Preparation and Synthetic Applications of Enantiomerically Pure Δ2-Pyrazolines
作者:José Barluenga、Félix Fernández-Marí、Argimiro L. Viado、Enrique Aguilar、Bernardo Olano、Santiago García-Granda、Carmen Moya-Rubiera
DOI:10.1002/(sici)1521-3765(19990301)5:3<883::aid-chem883>3.0.co;2-0
日期:1999.3.1
The [3+2] cycloaddition of alkenyl Fischer carbene complexes 1 and 6 with diazomethane derivatives to give Delta(2)-pyrazoline carbenes 2, 4, and 7 is described. The conversion of (-)-8-phenylmenthol-derived carbenes 6 into pyrazoline esters 9 through a one-pot cycloaddition-protection-oxidation is presented as an expeditious route to enantiomerically pure 3-alkoxycarbon-yl-Delta(2)-pyrazolines in good yields and in a highly regio- and diastereoselective manner. Pyrazolidines 13 were synthesized in excellent overall yields from 9 through pyrazolines 11 and 12, the diastereoselective reduction of C=N bond being the key step. Azaprolines 16 and 17 were prepared in very good yields from epimeric trans-13 or cis-13 by oxidative deprotection of the silylated hydroxy group. In an alternative reaction, the pyrazolidine ring of 13 was reduced to obtain protected open-chain 2,4-diamino alcohols 19 with three chiral centers.