3,4,5,6-Tetrahydrophthalimide: CAS 4720-86-9 (Acros)
4-Pentyn-1-ol: CAS 5390-04-5 (Acros)
Triphenylphosphine: CAS 603-35-0 (Sigma-Aldrich)
Diisopropyl azodicarboxylate: CAS 2446-83-5 (Alfa Aesar)
Tetrahydrofuran (anhydrous)

A solution of PPh₃ (1.05 eq, 21 mmol, 5.50 g) in anhydrous THF (100 mL) was cooled to -78^oC using an actone/CO₂ low temperature bath. To this cooled solution was added DIAD (1.04 eq, 20.8 mmol, 4.20 g, 4.04 mL) to give a yellow solution. The reaction was stirred for 1 hr at -78^oC and under N₂, after which time a white precipitate was observed. To this suspension was added the 4-pentyn-1-ol (1.25 eq, 25.4 mmol, 2.13 g, 2.32 mL) and the reaction was stirred for a further 20 min at -78^oC. After this time 3,4,5,6-tetrahydrophthalimide (1.0 eq, 20.0 mmol, 3.00 g) was added in one portion, the reaction was stirred at -78^oC for 1 hr before allowing to warm to RT. On warming to RT the precipitate was observed to disappear. Stirring at RT was continued for 16 hrs. The THF was removed in vacuo and the crude oil then redissoved in minimal Et₂O (approx. 10 mL). This solution was cooled in the freezer for 2 hrs before filtering under vacuum to remove precipitated triphenylphosphine oxide (Nb. if precipitation does not occur, scratching the vessels glass will encourage the process). The filtrate was concentrated in vacuo and purified by column chromatography (SiO₂, 10% EtOAc/Petrol) to give a colourless oil (4.28 g, 99%). 

This Mitsunobu procedure has been used with a variety of different alkyl alcohols, maleimide nucleophile and on varying scales (1 - 75 mmol). Yields range from 75-99%. The only example where the reaction has failed in my hands has been when coupling 3,4,5,6-tetrahydrophthalimide to methyl 6-hydroxyhex-2-ynoate.

Rf: 0.20 (20% Et₂0/Petrol); ¹H NMR (CDCl₃, 400 MHz) 3.58 (2H, t, J = 7.1 Hz, NCH₂), 2.33 (4H, m, CH₂CH₂C=C), 2.21 (2H, td, J = 7.1, 2.7 Hz, CH₂=CH), 1.96 (1H, t, J = 2.7 Hz, CH), 1.82 (2H, quin, J = 7.1 Hz, NCH₂CH₂).