Diethylaminosulfur Trifluoride (DAST)-Mediated Intramolecular Benzannulation of o-Allylchalcones: Synthesis of 3-Fluorotetralins

Abstract

A concise route for the synthesis of 3-fluorotetralines is described, including: (i) NaBH4-mediated reduction of oxygenated o-allylchalcones and (ii) sequential DAST-mediated intramolecular annulation of the resulting alkenols. A plausible mechanism is proposed and discussed. This protocol provides highly effective regio- and stereocontrolled allyl-enone cross-coupling to construct two stereocenters and one E-configured styryl group.

PdCl2/CuCl2/Bi(OTf)3‐promoted Construction of Sulfonyl Dibenzooxabicyclo[3.3.1]nonanes and Arylnaphthalenes via Intramolecular Annulation of Sulfonyl o‐Allylarylchromanones

“…The starting materials 2 and 3 were known compounds and the analytical data were consistent with those in the references [41–43] …”

“…[5] Additionally, skeleton 3 was synthesized from commercially available m-hydroxybenzaldehyde via a three-step synthetic route (O-allylation, Claisen rearrangement, O-alkylation) according to our previous reports. [41][42][43] To examine the Wacker-type aerobic oxidative annulation [44] of sulfonyl o-allylarylchromanones 4, our study commenced with the treatment of model substrate 4 a (R = Tol, Ar' = Ph, Ar = 3,4-(MeO) 2 Ph, 0.5 mmol) with a combination of PdCl 2 (10 mg, 5.6 mol%), CuCl 2 (94 mg, 1.4 equiv.) and Bi(OTf) 3 (100 mg, 15.2 mol%) in MeOH (20 mL) at 25°C for 5 h (Table 1, entry 1).…”

“…In Scheme 3, the starting sulfonyl 2‐allylarylchromanones 4 were prepared via Knoevenagel condensation of sulfonyl o ‐hydroxyacetocephenones 2 and o ‐allylbenzaldehydes 3 with yields in the range of 74%–86% in the presence of piperidine and HOAc under boiling toluene conditions for 10 h. Skeleton 2 was easily prepared from a two‐step synthetic route, including (1) CuBr 2 ‐mediated α‐bromination of o ‐hydroxyacetophenones 1 in refluxing EtOAc and (2) sequential nucleophilic substitution of the corresponding α‐bromo‐ o ‐hydroxyacetophenones with RSO 2 Na in a refluxing cosolvent of dioxane and H 2 O [5] . Additionally, skeleton 3 was synthesized from commercially available m ‐hydroxybenzaldehyde via a three‐step synthetic route ( O ‐allylation, Claisen rearrangement, O ‐alkylation) according to our previous reports [41–43] …”

“…The starting materials 2 and 3 were known compounds and the analytical data were consistent with those in the references. [41][42][43] A representative synthetic procedure of skeleton 4 is as follows: Piperidine (70 mg, 0.8 mmol) was added to a solution of 2 (1.0 mmol) and 3 (1.1 mmol) and in toluene (10 mL) at 25°C. The reaction mixture was stirred at 25°C for 10 min.…”

Diethylaminosulfur Trifluoride (DAST) Mediated Transformations Leading to Valuable Building Blocks and Bioactive Compounds

“…[1b] Chang and co-workers presented the synthesis of 3-fluorotetralins 98 by sequential DAST mediated intramolecular annulation of the alkenols 96 (Table 3). [48] The regio-and stereo-controlled fluorination procedure is a convenient reaction pathway through a chelated sixmembered transition state 97. As a result of the discussed transformation, only trans isomers of 3-fluorotetralins 98 were obtained.…”