Phenols

An approach to carbocyclic arenes by cyclative cleavage was presented only recently [38]. Merrifield resin was etherified with 3-hydroxypyridine (99), and the pyridine moiety was quaternized with bromoacetone to yield 100. Formation of an ylide 101 with NaOH/ethanol and subsequent reaction with a chalcone 102 produced the intermediates 103 after a Michael addition. A subsequent condensation reaction released the phenolates 104 from the solid phase under restoration of the pyridine moiety. Acidic work-up and filtration furnished 3,4,5-trisubstituted phenols 105 in yields varying from 52 % to 85 % (Scheme 27). Examples are shown in Table 1.

Procedure

Preparation of TOO: A solution of the sodium salt of 3-hydroxypyridine (22 g, 188 mmol) in DMA (100 mL) was added to Merrifield resin (20 g, 2.91 mmol/g) and stirred at 6070° C for 12 h.The resin 99 thus obtained was filtered and repeatedly washed withTHF, THF/water (1:1),THF, CH2CI2, and dried. Resin 99 (24.7 g) was added to the solution of 2-bromoacetone (16 g, 116 mmol) in acetonitrile (200 mL) and stirred at 70-78° C for 40 h. Resin 100 was washed as described above.

Preparation of phenols 105: Resin 100 (600 mg) and the corresponding chalcone 102 (0.29 mmol) were added to the solution of NaOH (14 mg) in EtOH (10 mL) and the mixture was stirred under reflux for 1 h.The resin was filtered off and washed as described

NaO.

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