3,4-dihydro-2H-pyran → 3-Methyl-4-(tetrahydropyran-2-yloxy)-1-butene

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Reaction Steps

To a suspension of magnesium turnings (50.4 g, 2.1 m) in ether (1500 ml) under a nitrogen atmosphere is added a solution of crotyl bromide (135.0 g, 1.0 m) in ether (125 ml), at room temperature over a period of four hours. The reaction mixture is then cooled to 0° C. and formaldehyde [formed by pyrolysis of paraformaldehyde (45.0 g, 0.5 ml)] is bubbled through the mixture. The resulting mixture is allowed to come to room temperature and stirred overnight. The reaction mixture is then decanted into a solution of ammonium chloride (212 g, 4.0 m) in ice water (2 l). The mixture is extracted with ether (2×3000 ml) and the combined ether extracts are dried (Na2SO4) and filtered. The solvent is removed in vacuo to give 57.2 g of 2-methyl-3-buten-1-ol (66%); nmr (CDCl3,δ): 0.99 (d, J=7 Hz, 3H, ##STR18## 2.10-2.70 (m, 1H, ##STR19## 3.30-3.60 (bd, J=6 Hz, 2H, ##STR20## 4.83-6.13 (m, 3H, vinyl protons); ir(neat): 3257, 1640 cm-1. (b) A solution of 2-methyl-3-buten-1-ol (54.16 g, 0.63 m), dihydropyran (52.92 g, 0.63 m), and p-toluenesulfonic acid (0.5 g) in ether (800 ml) is stirred at room temperature under a nitrogen atmosphere overnight. The reaction mixture is then diluted with ether (1 l) and washed with 5% sodium bicarbonate solution (1 l). The ether extract is dried (Na2SO4), filtered and solvent removed in vacuo to give 95.8 g of crude product. The crude product is purified by column chromatography on silica gel (500 g, hexane) to give (75%) 3-methyl-4-(tetrahydropyran-2-yloxy)-1-butene (80.62 g). ##STR21##

Provenance & Evidence