Cycloisomerization 1.5- hydrogen shift

Fiirstner and coworkers developed a new Pt- and Au-catalyzed cycloisomerization of hydroxylated enynes 6/4-141 to give the bicylo[3.1.0]hexanone skeleton 6/4-143, which is found in a large number of terpenes [317]. It can be assumed that, in the case of the Pt-catalysis, a platinum carbene 6/4-142 is formed, which triggers an irreversible 1,2-hydrogen shift. The complexity of the product/substrate relationship can be increased by using a mixture of an alkynal and an allyl silane in the presence of PtCl2 to give 6/4-143 directly, in 55 % yield (Scheme 6/4.36). 

An impressive example of the possibilities of metal complex photochemistry is the substantiation of the critical step in corrin synthesis reported by Eschenmoser 145> Ring closure is brought about by antara-facial cycloisomerization of a secocorrinoidic palladium complex by photochemical 1.16-hydrogen shift. 

Without additional reagents Cycloisomerization with 1,5-hydrogen shift... 

A regioselective transition metal-catalyzed cycloisomerization reaction of boron-containing alkynyl epoxides toward C-2- and C-3-borylated furans was developed. It was found that the copper catalyst as well as the gold catalyst with a relatively more basic triflate counterion favored boryl migration toward C-3-borylated furans, whereas employment of the cationic gold hexafluoroantimonate afforded C-2-borylated furans via a formal 1,2-hydrogen shift (14JA13146). 

Liu and coworkers reported the cycloisomerization of c -3-en-l-ynes to cyclopentadiene derivatives through 1,5-sigmatropic hydrogen shifts of catalytic ruthenium vinylidene intermediates (Scheme 44) [158]. 

Liu et al. reported a TpRuPPh3 (CH3CN)2-PF6-catalyzed cycloisomerization of cis-3-en-l-ynes I or their precursor alcohols 210, which afforded cyclopentadiene 211 (Scheme 80) [43]. Mechanistically, 210 undergoes ruthenium-catalyzed dehydration to afford the real substrates cis-3-en-l-ynes 1, which is converted into mthenium-vinyhdene intermediate H via [1,2]-shift of alkynyl hydrogen. A [1,5]-... 

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