Author: William D. ShipePublisher:
ISBN:
Category : Cyclobutane
Languages : en
Pages : 340
Book Description
The evolution of a convergent strategy that led to efficient, enantioselective syntheses of guanacastepene E and guanacastepene A (formal) is described. The first chapter of this thesis provides background information on (1) the isolation and biology of the guanacastepene family of secondary metabolites, (2) the substantial synthetic work carried out by other research groups toward their synthesis, and (3) the basis of our ultimate approach to the natural product. The synthesis of a fully functionalized C ring and two major model studies that provided critical information about the system are described in the second chapter. The final chapter describes (1) the enantiospecific synthesis of an A ring fragment from R-(-)-carvone, including a novel ring-contracting reaction, (2) the classical resolution of the C ring, and (3) the union of the two enantiopure fragments and further elaboration, culminating in the enantioselective total synthesis of both the natural (+)- and unnatural (-)-guanacastepene E and a formal total synthesis of (+)-guanacastepene A. The foundation of our convergent approach is the following sequence of three reactions: (1) the union of two functionalized building blocks through a [pi]-allyl Stille cross-coupling reaction, (2) the stereoselective construction of the C-11 quaternary carbon center with a [2+2] photocycloaddition, and (3) the stereoselective, reductive fragmentation of a cyclobutyl bond to form the seven-membered central B ring of the guanacastepenes.
