Convenient Access to meso Benzylic Bisalkynes

Abstract

meso-Bisalkynes and alkenes have potential as substrates for desymmetrization processes. The preparation of several meso-bis(1′-hydroxy-2′-propynyl)benzenes and their derivatives from phthalaldehydes using inexpensive and readily available reagents is described.

Key words

meso - desymmetrization - bisalkyne - phthalaldehyde

• References and Notes

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See also:
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• 11 1,2-Bis(prop-2-yn-1-ol)benzene 1a,b Ethynylmagnesium bromide solution (0.5 M in THF, 66 mL, 32.80 mmol) was added to a solution of o-phthalaldehyde (2.00 g, 14.93 mmol) in THF (75 mL). The mixture was heated to reflux with stirring for 4 h, and allowed to cool to room temperature. The reaction was quenched with sat. aq NH₄Cl (300 mL) and extracted with Et₂O (3 × 30 mL). The organic layers were combined and dried over MgSO₄, filtered, and the solvents removed under reduced pressure. The crude product was purified using column chromatography, eluting with EtOAc–PE (1:1) and using a vanillin dip to visualize the spots on TLC. A mixture of diastereoisomers was isolated as a yellow oil (2.47 g, 89%). The HNMR spectrum showed a mixture of isomers in a ratio of 2.1:1. The meso isomer was precipitated from the product mixture using CH₂Cl₂–PE, and was separated by filtration of the crystalline meso isomer and washing with PE. The (±)-isomer remained in the filtrate. Several precipitations were required to achieve almost complete separation. meso-(1S,1′R)-1,2-Bis-(prop-2-yn-1-ol)benzene (1a) Large colourless crystals (1.67 g, 60%), mp 98–99 °C. IR (neat): 3276, 3264, 2116 cm^–1. ¹H NMR (500 MHz, CDCl₃): δ = 7.92–7.77 (m, 2 H), 7.49–7.35 (m, 2 H), 5.91 (dd, J = 4.7, 2.2 Hz, 2 H), 2.95 (d, J = 4.7 Hz, 2 H), 2.74 (d, J = 2.2 Hz, 2 H). ¹³C NMR (126 MHz, CDCl₃): δ = 134.7, 129.7, 129.1, 80.3, 75.8, 62.7. Crystal data: C₁₂H₁₀O₂, M = 186.21, triclinic, a = 9.7265(12) Å, b = 10.6455(11) Å, c = 11.2471(7) Å, V = 980.67(19) ų, T = 173 K, space group P-1 (no. 2), Z = 4, 13495 reflections measured, 3562 unique (R _int = 0.0564), which were used in all calculations. The final wR2 was 0.1219 (all data). (±)-1,2-Bis-(prop-2-yn-1-ol)benzene (1b) Thick orange oil (0.79 g, 29%). IR (neat): 3414, 3287, 2117 cm^–1. ¹H NMR (500 MHz, CDCl₃): δ = 7.73–7.63 (m, 2 H), 7.41–7.37 (m, 2 H), 6.03 (d, J = 2.3 Hz, 2 H), 2.73 (d, J = 2.3 Hz, 2 H). ¹³C NMR (126 MHz, CDCl₃): δ = 137.7, 129.5, 129.3, 82.8, 75.8, 63.4.
• 12 Dale JA, Dull DL, Mosher HS. J. Org. Chem. 1969; 34: 2543