phenylalaninol, (S)- → rel-(1R,2R)-2-Methylcyclopropanecarboxylic acid

Beteiligte Stoffe

Reaktionsbedingungen

Reaktionsschritte

Racemic trans-2-methylcyclopropanecarboxylic acid (20 g, 0.2 mol) is dissolved in ethyl acetate (200 mL). (S)-2-Amino-3-phenyl-1-propanol [also known as (S)-phenylalaninol] (15.6 g, 0.103 mol, 0.51 equiv) is added in one portion, and the mixture heated to 65-70° C. After crystallization, which may be facilitated by seeding, the suspension is stirred at room temperature 20 h, then filtered; and the crystals are washed with ethyl acetate (2×15 mL). The crystals are dried at 40° C. under vacuum for 3 h: mass 18.4 g (37% molar yield, enantiomeric composition by chiral GC=85/15, chiral GC method below). The crystals are re-suspended in 370 mL ethyl acetate; the suspension is heated to reflux for 1 h, cooled to room temperature overnight, and the crystals filtered, washed and dried as above: mass 16.7 g (91% yield, chiral composition 96/4). A second purification in ethyl acetate (170 mL) as above affords (S)-2-amino-3-phenyl-1-propanol (R,R)-2-methylcyclopropanecarboxylic acid (1:1) salt (16.12 g, 96.5% yield, chiral composition 99/1=98% ee; 32% overall yield from racemic trans-2-methylcyclopropanecarboxylic acid).

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