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Synthesis and thermal electrocyclic reactions of substituted 7-(ethoxycarbonyl)bicyclo[4.2.0]oct-1(6)-enes

University of British Columbia

The a,β-acetylenic esters of general structure (18) were converted into the corresponding ethyl (E)- and (Z)-3-trimethylstannyl-2-alkenoates of general structures (133) and (134), respectively. Deconjugation-alkylation of ethyl (E)- and (Z)-3-trimethylstannyl-2-alkenoates (133) and (134) with alkylating agents of general structure (32) provided, stereo selectively, the functionalized esters of general structure (33). Palladium(0)-catalyzed intramolecular cross-coupling reactions of esters (33) provided the ethyl 2,3-bis(alkyhdene)cyclobutanecarboxylates of general structure (34) in good yields. The Diels-Alder reactions of the 1-substituted 2,3-bis(methylene)cyclobutanes (243) and ethyl 2,3-bis(alky]idene)cyclobutanecarboxylates of general structure (34) (R'=H) with the dienophiles TCNE and MVK were investigated. It was found that Diels-Alder reactions to prepare cycloaddition products (11), (14), (255-268) occurred with high face-and in some instances endo/exo- and regioselectivities. The conformations of some of these products (11), (14), (265-268) was determined by NMR analysis and a series of decoupling and NOE difference experiments. The torquoselectivity of the thermally-induced, conrotatory ring opening reaction of each of the bicyclic cyclobutenes (11), (14), (255-262), (264-268) to produce dienes of general structures (273) and (274) or (25) and (26) was investigated. Thermolysis of (262) produced only the product resulting from the outward rotation of the -CH₂OH group. Thermolysis of (255-262) and (264-268) produced mixtures of varying ratios of the outward (273) and inward (274) (or (25) and (26)) thermolysis products. The differing ratios of products was rationalized on the basis of electronic and/or steric factors. [Chemical Compound Diagrams]

Thesis/Dissertation

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2009-03-27

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http://hdl.handle.net/2429/6608

Chemistry

University of British Columbia

UBCV

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