A Cascade Approach to Naphthalene Derivatives from o‐Alkynylbenzaldehydes and Enolizable Ketones via in‐situ‐Formed Acetals

Abstract

Using the in‐situ‐formed acetal strategy, a facile approach has been developed to synthesize naphthalene derivatives from o‐alkynylbenzaldehydes and enolizable ketones. In situ acetal formation assists the condensation between o‐alkynylbenzaldehydes and enolizable ketones to give chalcone derivatives under Brønsted acidic conditions. In situ acetal formation facilitates the reaction by increasing the electrophilicity of the carbonyl carbon of the o‐alkynylaldehyde through oxonium ion formation, and also by enhancing the nucleophilicity of the α carbon of the ketone through the formation of an enol ether. The formed chalcones undergo trans to cis isomerization to effect alkyne–carbonyl metathesis to give naphthalene derivatives.

Silver‐Catalysed Domino Approach to 1,3‐Dicarbo‐Substituted Isochromenes

“…Ten years later, Sakthivel and Srinivarsan increased the selectivity of this transformation by using an In III salt as catalyst to produce the corresponding naphthyl ketones avoiding the formation of decarbonylation byproducts. Manojveer and Malaburugan obtained similar results in the presence of trimethyl orthoformate and a Brønsted acid such as triflic acid, but through a very different reaction mechanism: an in situ formed acetal assists the formation of a chalcone‐type intermediate, which, after trans/cis isomerization, undergoes a methanol‐assisted annulation. Conversely, Fan and Cheng, in more extensive work, were able to obtain selectively 1‐carbo‐substituted isochromene derivatives, albeit in fair yields, through an unprecedented cycloisomerization/addition path promoted by a simple Pd II salt …”

Applications of alkyl orthoesters as valuable substrates in organic transformations, focusing on reaction media

“…This transformation was initiated via the condensation of o-alkynylbenzaldehyde (515) with TMOF (4) by TfOH to obtain the in situ formed acetal (518), which was condensed with enol ether (519), arising from the reaction of ketones with TMOF, to form chalcone (520) which underwent intramolecular cyclization reaction to afford naphthyl ketones (517). 429 Manojveer and Balamurugan presented a facile and efficient process to get substituted benzo[a]uorenes (524), with regioselectivity via a domino three-component reaction of o-alkynylbenzaldehydes, alkynes, and TMOF by TfOH (20 mol%) in CH 3 CN or CH 2 Cl 2 at room temperature. This reaction proceeded through the reaction of aldehydes (515) with TMOF (4) by TfOH to obtain the in situ formed acetal (521).…”

Acid‐Acid‐Catalyzed Tandem Reactions Driven by an Additive‐Like Component

“…The naphthalene compounds can also be prepared from o ‐alkynylbenzaldehydes and enolizable ketones in a one‐pot manner (Scheme 50). [80] This method also employed HC(OMe) 3 as additive in conjunction with employing TfOH as a catalyst. In the initial stage, an oxonium ion intermediate I160 and enol ether 136 were formed, which were then converted into a chalcone‐type intermediate I161 with an elimination of two molecules of methanol.…”