Concerning methoxy substituent effect and topotactic assistance by methylene chain on photocyclization of n-methylene dicinnamates

Exploitation of sugar ring flipping for a hinge-type tether assisting a [2 + 2] cycloaddition

“…All the isomers are head-to-head adducts derived from 5 with the b-and d-isomers being E-E adducts and the n-isomer being a E-Z adduct as shown in Scheme 2. The regio-and stereoselectivities are comparable to those reported by others for tethered cinnamates, 4 though a few studies demonstrated the exclusive formation of b-and d-truxinates from the tethered dicinnamates 9 7 and 10, 8 respectively (Chart 1). Though the n-isomer is asymmetric, we were unable to elucidate the stereochemistry because neither the tethered-cycloadduct 7D nor the released-cycloadduct 8n could be separated from the other diastereomers.…”

“…A solution of compound 5 (30 mg, 0.071 mmol) in CHCl 3 (3 mL), which was bubbled with argon gas prior to the reaction, was irradiated for 44 h at 16 • C with a 500 W Hg(Xe) lamp (band-filtered at 313 nm). After removal of the solvent, the residue was chromatographed on silica-gel (toluene-ethyl acetate, 5 : 1) to give four fractions (Fr1, Fr2, Fr3, Fr4) each containing the isomeric mixture of methyl b-D-xylopyranoside-2,4-truxinates (7).…”

Effect of Substitution on the 2+2 Cycloaddition Reaction of Phenylpropanoids

“…Because of the strict steric requirements for photocyclization, irradiation of substituted cinnamic acids in solution produces only insignificant amounts of cycloaddition products and therefore topochemical assistance is required in order to probe the mechanism (5)(6)(7). It has been demonstrated that by varying the length of the methylene spacer group linking two cinnamic acid moieties, optimum separation of Ͻ4.0 Å with parallel alignment of the ␣-␤ unsaturated double bond can be satisfied by the preparation of dicinnamyl esters of propane 1,3-diol and butane 1,4-diol (8).…”

“…These were prepared by reacting butane-1,4-diol with 4-hydroxycinnamic acid (2), 4-hydroxy-3-methoxycinnamic acid (5), and 4-hydroxy-3, 5-dimethoxycinnamic acid (6). Although not naturally occurring within the plant cell wall, the 2-and 3-hydroxylated derivatives (4 and 3) have also been included.…”

“…Crystallization from ethanol afforded the corresponding methoxycarbonyloxycinnamic acids as white needles. mp 156-159ЊC, ␦ H ((CD 3 ) 2 CO) 3.86 (3H, s, OCH 3 ), 6.60 (1H, d, J (2H, d, J ϭ 16, C(7)H), 6.78 (4H, d, J ϭ 8.69, C(2,6)H), 7.44 (4H, d, J ϭ 8 (2H, d, J-16, C(8)H), 6.82 (2H, dd, J ϭ 7.8 and 1.9, C(6)H), 6.99 (2H, d, J ϭ 1.9, C(2)H), 7.03 (2H, dd, J ϭ 7.9 and 1.9, C(4)H), 7.2 (2H, t, J ϭ 7.8, C (5) Reaction with peroxidase. The substituted butane 1,4-dicinnamates (64 mmol) were dissolved in buffer/methanol (1:1) at pH 5, pH 7, and pH 9.…”