A Remeasurement of the Radiation Constant, h, by Means of by Duane W., Palmer H. H. PDF

By Duane W., Palmer H. H.

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The electrophilic sulfur- and tincentered radicals on their part would preferentially add to the electron-rich triple bond. Further β-lactams were obtained by a similar strategy starting from 2-azetidinone-tethered allene-ynes [151]. 4 Reactions Leading to the Formation of Polycyclic Compounds In a pioneering work, Curran et al. demonstrated the practicability of radical [4 + 1] annulations with isonitriles for the synthesis of cyclopenta-fused quinolines, a structural motive constituent of camptopthecin family antitumor agents [152, 153].

When a phosphine oxide was used, the reaction could be rerouted toward elimination of the heteroatom, and an original intramolecular vinylation sequence was observed (Scheme 31) [106]. The key elimination of β-phosphinoyl radicals is a reaction we discovered some time ago [64]. Thus, cyclohexylidene pyrrolidine 109 could be prepared in high yield starting from oxirane 108. As stated above, the reaction transited via radical 110. No tetrahydrofuran (THF) product was detected. Crich and Yao have exploited a homolytic substitution at sulfur to trigger a radical cascade that includes a loss of carbon monoxide and a radical fragmentation of a 4,6-O-benzylidene moiety to give esters such as 113 after a final diastereoselective reduction (Scheme 32) [107].

This outstanding result relies on initial carbonylation of alkyl radicals to form acyl radicals, such as 196. The nucleophilicity of acyl radicals allowed them to react with electrondeficient olefins to form α-cyano radicals (197), whose philicity is now reversed. Thus, they were able to add onto stannyl enolates and led to ketyl radicals such as 198. Those latter radicals underwent β-elimination of tributylstannyl radicals. This key elimination regenerated the mediator for the initial dehalogenation.

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A Remeasurement of the Radiation Constant, h, by Means of X-Rays by Duane W., Palmer H. H.


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