Tandem Claisen Rearrangement/6‐endo Cyclization Approach to Allylated and Pren­ylated Chromones

Abstract

Allyl, dimethylallyl and prenyl ethers derived from o‐acylphenols reacted upon microwave irradiation to form C‐allylated or ‐prenylated chromone derivatives, depending on the substitution pattern of the arene and the allyl substituent. The reaction proceeds through a tandem Claisen rearrangement and 6‐endo‐trig or 6‐endo‐dig cyclization sequence. For prenyl ethers, the tandem sequence can be extended by a Cope rearrangement to furnish 6‐prenylchromones. The method is potentially useful for the synthesis of natural products and drugs.

Functionalized Benzofurans via Microwave‐Promoted Tandem Claisen‐Rearrangement/5‐endo‐dig Cyclization

“…We started the investigation into the microwave‐promoted tandem sequence with precursor 4a , which was synthesized from 2‐allyloxybenzaldehyde ( 1a ) in two steps via carbonyl alkynylation using the Bestmann–Ohira reagent 2 , followed by Sonogashira coupling of 3a with iodobenzene. For the latter step, the copper‐free reaction conditions published by Liang et al were used (Scheme ).…”

Protecting‐Group‐Free Total Syntheses of Rubrolide R and S

“…The benzalde-hyde derivatives 3a [12] and 3b [13] as well as the required triflate 4 [14] can be synthesised by using literature-known protocols. The benzalde-hyde derivatives 3a [12] and 3b [13] as well as the required triflate 4 [14] can be synthesised by using literature-known protocols.…”

“…Building block 3b was synthesised in one step from 4hydroxybenzaldehyde 8 [13] (Scheme 3). Syntheses of building blocks 3a and 3b: a) tert-butyl (2-methylbut-3-en-2-yl) carbonate, Pd(PPh 3 ) 4 (1.0 mol-%), THF, 4°C, 16 h, 80 % (79 % [12] ); b) DMF, microwave, 180°C, 45 min, 88 %; c) isoprene, H 3 PO 4 , petroleum ether, room temp., 16 h, 52 % (51.3 % [13] ). Syntheses of building blocks 3a and 3b: a) tert-butyl (2-methylbut-3-en-2-yl) carbonate, Pd(PPh 3 ) 4 (1.0 mol-%), THF, 4°C, 16 h, 80 % (79 % [12] ); b) DMF, microwave, 180°C, 45 min, 88 %; c) isoprene, H 3 PO 4 , petroleum ether, room temp., 16 h, 52 % (51.3 % [13] ).…”

Oppenauer-type synthesis of α, β-acetylenic ketones from tetra(phenylethynyl)tin and aromatic aldehydes

“…α-Acetylenic ketones are highly reactive compounds widely used for the synthesis of various carbo-and heterocycles such as pyrroles [1], chromones [2,3], indenones [4], quinolones [5], benzodiazepines [6], spirocycles [7], etc. One of the most general methods for the synthesis of α-acetylenic ketones is based on the reaction of metal acetylides with aldehydes, followed by oxidation of propargyl alcohols formed [2,5,[8][9][10][11].…”

“…One of the most general methods for the synthesis of α-acetylenic ketones is based on the reaction of metal acetylides with aldehydes, followed by oxidation of propargyl alcohols formed [2,5,[8][9][10][11]. Trialkylstannylacetylenes Alk3Sn-C≡C-R are tolerant with respect to many functional groups, therefore they are actively used as alkynylating reagents as well as reagents in crosscoupling reactions [12,13].…”