Effect of >CO···H–Ar interaction on endo/exo selectivity in the Diels–Alder reaction of phenyl-substituted cyclopentadienones

Thermodynamic and kinetic parameters associated with the fluxional behavior of 2-methyl- and 2,6-dimethyltroponeiron tricarbonyl complexes

“…The mixture was stirred at room temperature under argon for 30 min. Under this conditions, the first formed tricarbonyl [ (1,2,3,4,5-g)-1-methyl-7-oxocyclohepta-2,4-dien-1-yl]-iron(1+) tetrafluoroborate 2 rapidly isomerised to the thermodynamically more stable tricarbonyl [(1,2,3,4,5-g)-1-methyl-7-oxocyclohepta-2,4-dien-1-yl]iron(1+) tetrafluoro-borate 3. The obtained tricarbonyliron salts 3 and 2 were precipitated by addition of dry Et 2 O (4.0 ml) to the reaction mixture.…”

“…Yield: 1.34 g (4.88 mmol, 66%). 1 H NMR (CDCl 3 ): 6.41 (1H, dq, J ð3; 4Þ ¼ 8:4, J ðMe-Cð2Þ; 3Þ ¼ 1:5, H-C(3)), 6.18 (1H, dd, J ð4; 5Þ ¼ 7:4, J ð5; 7Þ ¼ 1:7, H-C(5)) [21], 3.23 (1H, d, J ð5; 7Þ ¼ 1:7, H-C (7)), 2.53 (3H, s, Me-C(6)), 2.50 (1H, dd, J ð3; 4Þ ¼ 8:4, J ð4; 5Þ ¼ 7:4, H-C(4)), 1.47 (3H,d,3Þ ¼ 1:5,). 13 C NMR (CDCl 3 ) [22]: not detectable at ca 208 (s, 3Â CO from Fe(CO) 3 ), 198.8 (s, C@O), 144.2 (d, C(3)), 128.3 (s, C(2)), 108.5 (s, C(6)), 94.9 (d, C(5)), 65.2 (d, C (7)), 47.8 (d, C(4)), 24.1 (q, Me-C(2)), 16.9 (q, Tricarbonyl[(4,5,6,7-g)-2,6-dimethyltropone]iron 5 (20.0 mg, 0.073 mmol, 1.0 mol eq.)…”

“…They have found use as dienophiles in Diels Alder [1] and other electrocyclisation reactions [2] and in the preparation of heterocycles [3]. Iron tricarbonyl complexes of tropones, which are readily available by treatment of tropones with Fe 2 (CO) 9 [4], have been used in the synthesis of hydroazulenes related to the pseudoguaianolide class of terpenes by [3 + 2] cycloaddition reactions [5].…”

Synthesis of 2,6-Dimethyltropone - A New, Convenient Methodology from 2,6-Dimethylcyclohexanone

“…Yield: 991.9 mg, 7.39 mmol (69%); yellow oil; bp 120°C/0.12 mbar. 146.41 [2´ s, C(2) and C(6)], 131.94 [d, C(7)], 134.32 [d, C(4) or C (5)], 135.99 [d, C(3)], 139.11 [d, C(5)…”

“…as dienophiles in Diels-Alder 5 and other electrocyclisation reactions, 6 and in preparation of heterocycles. 7 As part of a program for the synthesis of pseudoguaianolide terpenes, especially the antivairal compounds reiswigin A and B 8 (Figure 1) by metal assisted [3 + 2] cycloaddition reactions, 9 we developed and optimised a new, convenient method for the synthesis of 2,6-dimethyltropone (5) in overall 52% yield (Scheme 1). For starting material, the synthesis uses commercially available 2,6-dimethylcyclohexanone (Aldrich) -as a mixture of syn and anti isomers (80:20, respectively).…”