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The origin of the fluorinative [4+3] cycloaddition in the course of [4+3] cycloaddition of butyne-1,4-diether-Co2(CO) 6 complex 75a was investigated. The fluorinated cycloadduct 76a was found to come from the initial destannylation of silylstannane 59 to give allylsilane 113. This destannylation is facilitated by [EtO-BF3]-, which is formed in the course of normal [4+3] cycloaddition. The resultant allylsilane 113 then reacts with the substrate 75a in the presence of BF 3-OEt2 to form 76a via a cyclic 2° alkyl cationic intermediate 117. Despite the extreme sensitivity of [4+3] cycloaddition to the moisture, the normal cycloadditions free of fluorination were performed successfully with substrates 75a and 111 . In the [4+3] cycloaddition of 111 with 59, regioisomeric mixture of cycloadducts 69b and 69b ' was obtained in a ratio of 69b:69b' = 1:1.3. This is in comparison with a regioisomeric ratio of 69b:69b' > 30:1, obtained with substrate 68d. It was found that the substitution at the propargyl site and the bulkiness of the alkoxy group in the substrates are the major factors in determining the sequence of the two steps in the normal [4+3] cycloaddition. Substantial efforts were focused on the trapping reactions of the cationic intermediate 117 and its methyl- and phenyl-substituted analogues, obtained by the use of the allyltrimethylsilane. Various trapping nucleophiles were employed, such as "F-", "Cl-", "Br -", benzene, toluene and chlorobenzene. The resultant trapping products 125a, 125b, 125c, 127a, 127b, 127c, 129, 130a, 130b, 130c, 135a and 135b were produced; good yields were achieved in most cases. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2001 .L8. Source: Masters Abstracts International, Volume: 40-03, page: 0710. Adviser: James R. Green. Thesis (M.Sc.)--University of Windsor (Canada), 2001.
Lu, Yafan., "[4+3] Cycloadditions and tandem [4+3] cycloaddition/nucleophilic trapping reactions of propargylic diether dicobalt complexes via sequential Nicholas reactions." (2001). Electronic Theses and Dissertations. 506.