Synthesis and some related studies of alkyl 2,3-bis(alkylidene)cyclopentanecarboxylates

• Main Author: Wong, Timothy
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/7021

With the use of lithium (trimethylstannyl)(cyano)cuprate (123), α, β -acetylenic esters of general structure 100 were converted into the corresponding alkyl (E)- and (Z)-3- trimethylstannyl-2-alkenoates 89 and 91. Homoallylic diiodides of general structures 98 and 99 were synthesized, via a sequence of transformations, from the corresponding esters 89 and 91, respectively. Deconjugation-alkylation of ailcyl (E)- and (Z)-3-trimethylstannyl-2- ailcenoates 89 and 91 with electrophiles 96 and 97, provided, stereoselectively, the functionalized esters of general structure 206. Palladium(0)-catalyzed intramolecular cross-coupling reaction of esters 206 provided alkyl 2,3-bis(alkylidene)cyclopentanecarboxylates of general structure 219 in good yields and in a stereochemically defmed fashion. Thus, a general strategy for the preparation of alkyl 2,3-bis (alkylidene)cyclpentanecarboxylates possessing E,E-, E,Z- and Z,Z configurations (i.e. 81,82 and 84) was established. The limitations of this palladiumcatalyzed intramolecular coupling reaction were shown by the inability to provide the Z,E diene 230 in a stereocontrolled manner, and by the low yield obtained in the preparation of 229. The dihedral angles between the two exocycic C=C bonds in the (Z,Z)-diene system of general structure 84 were determined by X-ray crystallographic analysis of crystalline derivatives of alkyl (Z,Z)-2,3-bis(alkylidene)cyclopentanecarboxylates 222, 228 and 229. The magnitude of the dihedral angles in compounds 237,238,241, 243 and 247 ranges from 48.6° to 58.00. A new CuCl-mediated intramolecular coupling reaction of vinyl halide and vinyltrimethylstannane functions was discovered in conjunction with studies directed toward the synthesis of the Z,E-diene 230 in a stereochemically defined manner and toward the optimization of the yield in the preparation of 229. This method has been applied successfully to the preparation of a number of alkyl 2,3-bis(alkylidene)cyclopentanecarboxylates possessing E,E-, E,Z-, Z,E- and Z,Z-configurations (81,82,83 and 84) and to the synthesis of a variety of bicydic compounds containing a conjugated diene system (253,289-293). A provisional mechanism was proposed for this new coupling procedure. The Diels-Alder reactions of the dienophiles TCNE and MVK with the alkyl 2,3- bis(alkylidene)cyclopentanecarboxylates of general slructure 219 as well as the related dienes of general structure 314 were investigated. It was found that these Diels-Alder reactions occur with high face-, endo/exo- and regioselectivities. [chemical compound diagrams] === Science, Faculty of === Chemistry, Department of === Graduate