Interrupted Carbonyl‐Alkyne Metathesis

Abstract

Carbonyl-olefin metathesis and carbonylalkyne metathesis represent established reactivity modes between carbonyls, alkenes, and alkynes under Lewis and Brønsted acid catalysis. Recently, an interrupted carbonyl-olefin metathesis reaction has been reported that results in tetrahydrofluorenes via a distinct fragmentation of the reactive intermediate. We herein report the development of an analogous transformation interrupting the carbonylalkyne metathesis reaction path resulting in dihydrofluorene products relying on Lewis acidic superelectrophiles as active catalytic species.

Oxophosphonium-alkyne cycloaddition reactions: reversible formation of 1,2-oxaphosphetes and six-membered phosphorus heterocycles

“…The metathesis reaction between carbonyls and alkynes is a powerful method for the synthesis of α,ß-unsaturated ketones and has received much attention in the construction of heterocycles and in natural product synthesis. − This well-understood reaction involves an oxete intermediate, which is unstable toward ring opening and the formation of the enone product (Scheme a) . Since carbonyl–alkyne [2 + 2] cycloadditions are orbital-symmetry forbidden in the ground state, either photo-irradiation or the use of a catalyst , has been established as an avenue to overcome the kinetic barriers.…”

Oxetanes and Oxetenes: Fused-Ring Derivatives

“…Carbonyl-alkyne metathesis reactions are powerful tools to build in a straightforward manner a,b-unsaturated carbonyls through the cycloreversion of oxetenes intermediates. [80][81][82][83][84][85] As evocated before, metal-catalyzed cyclization reactions of w-alkynyl carbonyls constitute efficient transformations for the synthesis of a,b-unsaturated ketones or aldehydes. As an example, Yamamoto 86 reported the gold-catalyzed carbocyclization 87 of a series of internal ketones 63 that delivered enones 66 in good to excellent yields.…”

“…06.11.6 (+)-PleuromutilinCarbonyl-alkyne metathesis reactions[80][81][82][83][84][85] have found numerous applications in the context of total synthesis of natural products and only a few examples will be discussed here. During the course of investigations aiming at the total synthesis of (+)-pleuromutilin, Herzon reported the unexpected formation of the transient intermediate fused oxetene 230 from the oxidative cyclization/C-O reductive elimination of yne-aldehyde 227 using Ni(COD)2 (40 mol%), 4,5-dichloro-1,3-bis(2,6diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene (40 mol%) and triisopropylsilane as a reductant.…”

Synthesis of Dibenzotropones by Alkyne-Carbonyl Metathesis

“…While olefin metathesis reactions have been widely reported in the literature, alkyne-carbonyl metathesis (ACM) reactions are more rare and have in recent years emerged as a versatile synthetic tool for the construction of α,β-unsaturated carbonyl compounds with 100% atom economy . The ACM reaction has been reported to be catalyzed by various Lewis and Brønsted acids such as AgSbF 6 , FeCl 3 , Yb­(OTf) 3 , In­(OTf) 3 , CuI/I 2 , TfOH, and many others. The intramolecular (ring-closing) ACM allows the formation of various carbo- and heterocycles that are not easily available by traditional procedures. The formation of conjugated enones via ACM reaction is dependent on the type of catalyst (Scheme ).…”