Ein kurzer, atomökonomischer Zugang zu Tetrahydroxanthenonen

Abstract

Die Verwendung von Wasser bei der Domino‐Michael‐Addition‐Aldolkondensation von Salicylaldehyden wie 1 als Nucleophil und Carbonylkomponenten wie 2‐Cyclohexen‐1‐on (2) als Michael‐Acceptor liefert 2,3,4,4a‐Tetrahydroyxanthen‐1‐one wie 3 in sehr guten Ausbeuten.

A Novel Enantioselective Catalytic Tandem Oxa‐Michael–Henry Reaction: One‐Pot Organocatalytic Asymmetric Synthesis of 3‐Nitro‐2H‐chromenes

“…Use of salicylaldehyde with no substitution gave the chromene derivatives in relatively high yields and moderate enantioselectivities (Table 4, entries [1][2][3][4]. When introducing the substituted salicylaldehydes (Table 4, entries 5-8), the domino reactions afforded the corresponding products with higher enantioselectivites, which demonstrated the reactions were more selective with the steric interaction increasing.…”

“…[1] Accordingly, interest in developing syntheses of these privileged structures continues to grow, [2] especially concerning condensations between salicylaldehyde derivatives and Michael acceptors such as a,b-unsaturated aldehydes (ketones) and nitroalkenes which have proven to be a versatile strategy to the benzopyan moiety. [3] Furthermore, for obtaining chiral chromenes, an enantioselective tandem Michael-aldol reaction of salicylaldehyde derivatives with a,b-unsaturated aldehydes (ketones) catalyzed by proline derivatives was developed by Wang, Arvidsson, Córdova and their co-workers, respectively. [4] Nevertheless, a chiral amine catalytic tandem oxa-Michael-Henry reaction of salicylaldehyde derivatives with nitroolefins for chiral 3-nitro-2H-chromene derivatives has not been researched.…”

Base-Catalyzed Condensation of 2-Hydroxybenzaldehydes with α,β-Unsaturated Aldehydes - Scope and Limitations

“…After adding 415 mg (4.93 mmol) of senecialdehyde (6a) the mixture was placed in a sonication bath for 2.5 days. The crude product was extracted with 3 Â 15 mL of Et 2 O and the combined organic phases were dried over MgSO 4 . Purification by column chromatography (EtOAc/PE, 1/5) gave 15g as yellow needle-shaped crystals; yield: 434 mg (40%), mp 56 -58 8C, R f (cyc/EtOAc, 5/1) ¼ 0.55.…”

“…Therefore different protocols have been described, varying in solvent (t-BuOH, CHCl 3 /H 2 O, dioxane, water only) and base (t-BuOK, K 2 CO 3 , DABCO) used. [3] The application of this concept on 2-cyclohexen-1-one (4) to yield tetrahydroxanthenones as seen in 5 has been recently and independently reported by us [4] (Scheme 1) and the Kim group. [5] Most closely related to these protocols is the procedure described by Ravichandran.…”

“…The aforementioned reaction conditions [4] were used to test 2-hydroxybenzaldehyde (3a) in the condensation reaction with senecialdehyde (6a) as a model system. The condensation product 7a was isolated in 57% yield.…”