52. Phenylpropiolic acids. Part I. The dimerisation of o-methoxyphenylpropiolic acid

Improved Methods of Synthesis of Lignan Arylnaphthalene Lactones via Arylpropargyl Arylpropiolate Esters

“…We next examined the application of these improved experimental conditions to the synthesis of the natural piperonyl analogues, justicidin E [9], first isolated fromJusticia procumbent (31), and taiwanin C [10], first isolated from Taiwania cryptomeriodes (32). The intermediate diynic ester [17] required for this purpose was obtained in the following way. Piperonal was treated with triethyl phosphonoacetate under the conditions devised by Wadsworth and Emmons (33) for formation of propiolate esters; this yielded ethyl 3,4-methylenedioxyphenylpropiolate [15] which was then reduced with diisobutylaluminium hydride to yield 3,4-methylenedioxyphenylpropargyl alcohol…”

“…3.4-Methylenedioxyphenylpropargyl 3,4-methylenedioxyphenylpropiolate [17].-3,4-Methylenedioxyphenylpropiolic acid [11] (600 mg) was added to freshly distilled thionyl chloride (4 ml) at room temperature until solution was complete (3 h). Excess thionyl chloride was removed by repeated addition of C^H^a nd evaporation under reduced pressure.…”

“…The residual oil product (1.06 g) was chromatographed on neutral alumina, and elution with Et20-petroleum ether (1:1) gave the ester 17 as an oil that crystallized from Et2Q as a colorless solid (1.0 g): mp 135-138°; ir v (CHC13) 2225 (C = C), 1722 (C=D) cm-1; *H nmr (CDC13) 4.99 (s, CH2), 5.95 and 5.98 (s, two OCH20 groups), 6.61-7.31 (m, six ArH). Intramolecular cyclization of 3,4-methylenedioxyphenylpropargyl 3,4-methylenedioxyphenylpropiolate [17].-Isolation of belioxanthin [18], justicidin E [9], taiwanin C [10] and ret robelioxantbin [19].-A solution of the ester 17 (500 mg) in xylenes (5 ml) was heated under reflux for 5 h and the solvent removed under reduced pressure. The residual oil [two broad spots, Rf 0.68 and 0.57 on tic analysis on silica with hexane-EtOAc (4:1)] was subjected to flash chromatography on Si gel with hexane-EtOAc (4:1) under a positive pressure of N2 with 20-ml aliquots being collected and assayed by tic in the same manner as above.…”

“…54 and 0.50) which was re-subjected to flash chromatography as before. Fractions [16][17][18][19][20][21][22][23][24][25][26][27][28] gave further taiwanin C (90 mg), and fractions 29-53 gave an oil (87 mg, RfO. 54 and 0.52).…”

“…In the earliest procedure, dating from 1895 (12), the product obtained by heating phenylpropiolic acid [31 with Ac20 under reflux proved to be 1-phenylnaphthalene-2,3-dicar boxylic anhydride [4] (13)(14)(15)(16)). The general applicability of this procedure for many phenylpropiolic acids is now established, notably in the work of Baddar and coworkers (17). In cases where the severity of the conditions resulted in undesirable side reactions, it was shown that the desired self-condensation could be obtained at 0°b y treatment of the arylpropiolic acid with N,N-dicyclohexylcarbodiimide (18,19), and the scope of this procedure modification has been explored (20).…”