Abstract
The formal (4+3) cycloaddition of 1,3‐dienes with Rh(II) and Au(I) non‐acceptor vinyl carbenes, generated from vinylcycloheptatrienes or alkoxyenynes, respectively, leads to 1,4‐cycloheptadienes featuring complex and diverse substitution patterns, including natural dyctiopterene C′ and a hydroxylated derivative of carota‐1,4‐diene. A complete mechanistic picture is presented, in which Au(I) and Rh(II) non‐acceptor vinyl carbenes were shown to undergo a vinylcyclopropanation/Cope rearrangement or a direct (4+3) cycloaddition that takes place in a non‐concerted manner.
Highlights
The formal (4 + 3) cycloaddition of 1,3-dienes with Rh(II) and Au(I) non-acceptor vinyl carbenes, generated from vinylcycloheptatrienes or alkoxyenynes, respectively, leads to 1,4-cycloheptadienes featuring complex and diverse substitution patterns, including natural dyctiopterene C’ and a hydroxylated derivative of carota-1,4-diene
Davies and coworkers pioneered the reaction of 1,3-dienes with donoracceptor vinyl carbenes, generated from diazo compounds, to give cycloheptadienes after cyclopropanation and Cope rearrangement, through an overall formal (4 + 3) cycloaddition process (Scheme 1, B).[8]
We report the reactivity of these catalytically-generated intermediates with 1,3-dienes to give a diverse range of 1,4-cycloheptadienes through a (4 + 3) formal cycloaddition process
Summary
To diazo compounds,[10] limiting the methodologies to the use of acceptor metal carbenes.[11] Different gold(I)-catalyzed (4 + 3) cycloadditions were developed over the years, mainly based on the reaction of 1,3-dienes with allenes[12] or vinyl carbenes generated from propargyl esters,[13] cyclopropenes[14] or by recombination of linear dienediynes.[15] In our pursuit to identify new sources of non-acceptor metal carbenes, we have established both 7-vinyl-1,3,5-cycloheptatrienes (1) and 5alkoxy-1,6-enynes (6) as suitable precursors The former can undergo metal-catalyzed retro-Buchner reactions (releasing aromatic units),[16] and the latter can take part in a gold(I)catalyzed cycloisomerization/migration cascade sequence[17] generating non-acceptor vinyl carbene intermediates with diverse substitution patterns (Scheme 1, C).
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