B. (3-Methyl-2-butenyl)(2-propynyl)propanedioic acid, dimethyl ester (2). To a 1-L, flame-dried, three-necked, round-bottomed flask, equipped with a magnetic stirring bar (Note 6) and under an argon atmosphere, is added 9.0 g (0.19 mol) of sodium hydride dispersion (Note 7). The sodium hydride is <washed> with <petroleum ether> (4 × 30 mL), <removing> the petroleum ether by pipette after the <sodium hydride> has settled. The <flask> is then fitted with a <thermometer> and an over-dried pressure-equalizing addition funnel and <charged> with 500 mL of tetrahydrofuran (Note 7). The heterogenous mixture is <cooled> with an <ice bath>, and 36.4 g (0.18 mol) of the monoalkyl diester (1) is added dropwise at the rate of 1 drop/2–3 sec (Note 2). The cooling bath is <removed> when the addition is complete, and the solution is <stirred> until no more <gas> evolves (ca. 1 hr). The reaction mixture is recooled to <0°C>, and 22 mL of propargyl bromide solution (0.20 mol) (Note 7) is added dropwise while the temperature is maintained at 0–10°C. Sodium bromide begins to <precipitate> within <20 min>. The ice bath is <removed>, and the reaction mixture is <stirred> <overnight> (Note 8). After careful addition of 50 mL of <water> (Note 9) and removal of the <stirring bar>, the solution is <transferred> to a 1-L, one-necked, round-bottomed <flask> and concentrated with a <rotary evaporator>. The residue is taken up in 500 mL of ether and <washed> with <water> (3 × 300 mL) and saturated <salt solution> (1 × 100 mL). The aqueous layers are combined, saturated with salt, and <extracted> with <ether> (2 × 150 mL). The ether layers are combined, dried over magnesium sulfate, filtered, and <concentrated> with a <rotary evaporator>. The residue is distilled through a short-path <distillation> apparatus at <80°C> (0.25 mm) to yield 34.0–34.2 g (79–80%) of (Note 10).