A procedure was developed for preparing acetylenic esters of bicyclo[2.2.1]hept-5-ene-2-carboxylic acid. The structures of the compounds were confirmed by IR and 1 H NMR spectroscopy. The Kovats indices of the compounds were determined, and their boiling points were estimated by gas3liquid chromatography. The protective properties of the esters against acid corrosion of steel were studied.Norbornene derivatives exhibit various useful properties. Thanks to their rigid framework structure, these compounds with fixed substituents are promising models for studying structure3property relationships [1]. Some norbornene derivatives exhibit analgetic, antiseptic, and antiphlogistic properties [2,3]. Of particular interest are acetylenic esters of norbornenecarboxylic acid. On the one hand, they have valuable properties themselves; on the other hand, they are promising as synthetic precursors of diverse valuable compounds owing to the combination of reactive norbornene and acetylenic fragments [4].The synthesis of propargyl norbornenecarboxylate by esterification of norbornenecarboxylic acid with propargyl alcohol in the presence of Brønsted acid catalysts was described in [5]. However, the yield (30%) and purity (88%) of the target product were poor.Proceeding with studies concerned with synthesis of acetylenic esters of norbornenecarboxylic acids [6 38], we developed a convenient synthetic route to these compounds and examined their protective properties against acid corrosion of metals. The compounds were prepared by reactions of bicyclo[2.2.1]hept-5-ene-2-carboxylic acid chloride I with acetylenic alcohols II!IV:
II!IV I V !VIIwhere R 1 = R 2 = H (II, V); R 1 = Me, R 2 = H (III, VI); R 1 = Me, R 2 = CH=CH 2 (IV, VII).The reaction with primary alcohol II occurs at room temperature with heat liberation and is complete in 0.5 h. With tertiary alcohols III and IV, the reaction is less facile, and the corresponding esters VI and VII were obtained by heating at 80oC for 5 h. The yield of the target products was 90 396%.The structure of esters V3VII was confirmed by independent synthesis. First, we prepared acetylenic acrylates IX!XI by a reaction of acryloyl chloride with acetylenic alcohols II3IV. This was followed by the Diels3Alder addition of cyclopentadiene VII to acrylates IX!XI to obtain compounds V3VII:; CO 2 ÄCÄCÄCÄR 2 6 V!VII , Ä Ä g g g g R 1 R 1 + K S Q ? IX!XI VIII (2)where R 1 = R 2 = H (IX); R 1 = Me, R 2 = H (X); R 1 = Me, R 2 = CH=CH 2 (XI).The constants of compounds IV3VII prepared by both procedures are identical; they are listed in Table 1. The compositions and structures of the compounds were also confirmed by elemental analysis and by IR (Table 1) and 1 H NMR spectroscopy. The IR spectra of V3VII contain the stretching vibration bands (cm !1 ) of C=O (1730 31740), C3O (122531240) and C=C (2160 32165) groups. The band at 3290 cm !1 in the spectrum of V is characteristic of the =C3H bond. The stereoisomers of V and VII have similar IR spectra, with the absorption bands of the double bond in the norbornen...
