Thallium(III) nitrate oxidation of chromens: cis-dihydroxylation and dialkoxylation

Thallium trinitrate-mediated ring contraction of 1,2-dihydronaphthalenes: the effect of electron-donating and electron-withdrawing groups

“…These values agree with that observed for the cis-and trans-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene and other related cis isomers, 35 as well as with the cis-1,2dimethoxychroman 61 ( Figure 2). 32 However, the values are not in accord to that determined by Ogibin et al for the cis-and trans-1,2-dimethoxy-1,2,3,4-tetrahydronaphthalenes. 36 Nitrate derivatives are not usually produced in the oxidation of olefins with TTN, although a few papers reported the isolation of these compounds.…”

“…The resulting oil was purified by flash chromatography (silica gel 200-400 mesh, eluent: EtOAc (90%) and hexanes (10%)) affording the indan 32 (0.148 g, 0.527 mmol, 52%), 33 (0.0322 g, 0.115 mmol, 11%), 34 (0.0050 g, 0.018 mmol, 2%) and a mixture of the 35 and 36. (32 Oxidation of 20 with TTN. The reaction was performed following the general procedure, but using 20 (0.16 g, 0.72 mmol), MeOH (4.6 mL) and TTN.3H 2 O (0.35 g, 0.79 mmol), which was added at 0 °C.…”

Synthesis of the phytoalexin (±)-phaseollin: 3-phenylthiochromans as masked 2H-chromenes and o-prenyl phenols

“…thiophenol (1 7.18 g), and azoisobutyronitrile (0.5 g) were refluxed in dry benzene (150 cm3) for 48 h. The solution was diluted with ether and washed with aqueous sodium hydroxide, water, and brine. Evaporation of the solvents gave a solid residue which was crystallised from ethyl acetate-light petroleum to give the title compound (14.5 (9).-The sulphide (8) (104 mg) in dichloromethane (15 cm3) was cooled to 0 °C and treated with mchloroperbenzoic acid (123 mg) in dichloromethane (5 cm3). The solution was allowed to warm to room temperature and set aside for 20 h. The solution was washed with aqueous sodium metabisulphite, dried, and evaporated.…”

“…The regiochemistry of addition follows most clearly from the subsequent chemistry of the product (see below); none of the isomeric 4-phenylthiochroman was detected. Oxidation of the sulphide (8) with m-chloroperbenzoic acid gave the corresponding sulphone (9). A similar addition reaction to the chromene (3) also gave a single chroman (10) (85%).…”

Structural requirements for the thallium(III)-mediated cyclisation of unsaturated alcohols. A novel fragmentation reaction producing 19-norsteroids

“…Since the thallium(rI1)-mediated cyclisation is also believed' to require anchimeric assistance for the second step (as shown in Scheme 1) it was of interest to explore the reactivity of (4) for which this assistance was precluded for the silver-assisted iodination.? Hence, 19-hydroxy-5-cholestene (4) was treated with Tl(N03)3.3H20 in 1 ,Zdimethoxyethane (DME) and, surprisingly, an instantaneous reaction occurred even at -20°C producing essentially a single compound in an 81% isolated yield, later identified as the 10P-hydroxy-10-norsteroid (7) by a single-crystal X-ray analysis (Figure l). $ Similarly, when the reaction was carried out with anhydrous (CF&02)3T1 in MeOH, the corresponding methoxy-derivative (8) was obtained, although in an appreciably lower yield (27%).…”