Catalyzed cycloaddition reactions of α-silyloxy-α,β-unsaturated ketone and aldehyde

Formal Enantioselective [4+3] Cycloaddition by a Tandem Diels–Alder Reaction/Ring Expansion

“…[5] Most similar to our system is the Lewis acid-catalyzed [4 + 3] cycloaddition of 2-siloxyacroleins with dienes, which has been proposed to involve a stepwise process, in which the zwitterionic intermediate goes directly to the [4 + 3] cycloadduct. [21][22][23] Even though it has been shown that the Diels-Alder cycloadduct derived from cyclopentadiene and a 2-siloxyacrolein rearranges cleanly to the formal [4 + 3] cycloadduct, [18] computational studies suggest that this process occurs by a retro DielsAlder reaction followed by a [4 + 3] cycloaddition. [24] Therefore, we decided to conduct further studies to understand how the [4 + 3] cycloadducts in the reaction of 2-alkylacroleins and cyclopentadiene are formed.…”

“…Such a ring closure of 19 would be much more reasonable when R is siloxy, especially if it is also accompanied by a silyl migration. [21][22][23] …”

Lewis acid complexes of 1,2-diketones and their derivatives. The synthesis of seven-membered rings

“…[ l ] . Indeed, as this work was underway, Sasaki et al reported that such a reaction occurs with the SnC1,-catalysed reaction of 1,3-butadiene with trimethylsilyl ether of pyruvaldehyde (5).…”

Masked Ketenes as Dienophiles in the Diels–Alder Reaction

“…Several known ketene equivalents have not been discussed throughout the present review, such as acrylic acid (93), [95,96] silyl enol ether 94, [97] a-thioacrylate 95, [98] phenylseleno acetylene 96, [99] and acetoxymaleic anhydride (97), [100] to name only a few (Scheme 14). As far as we are aware, none of these examples (or any other masked ketene equivalents not covered) have been applied outside simple settings.…”