Abstract
Syntheses of anti (1a) and syn (1b) isomers of CpMo(CO) 2 (η 3 -1-methyl-2-(methoxycarbonyl)-allyl) are described. Sequential addition of NOBF 4 and LiCl to 1a or 1b at -40°C preferentially produced CpMo(NO)Cl(η 3 -1-anti-methyl-2-(methoxycarbonyl)allyl) (3a) or CpMo(NO)Cl(η 3 -1-syn-methyl-2-(methoxycarbonyl)allyl) (3b), respectively. The variable-temperature 1 H NMR spectra (CDCl 3 , -60°C) of 3b show the presence of endo and exo conformers, between which mutual exchange was observed. Stirring mixtures of 3a and 3b (3a/3b = 85/15 to 11/89) with PhCHO in CH 2 Cl 2 /CH 3 OH (20°C, 24 h) gave trans-2-methylene-3-methyl-4-phenylbutyrolactone (4a) as the major product in addition to (1S*,2R*)-1-phenyl-2-methyl-3-(methoxycarbonyl)-3-buten-1-ol (4b). Compound 4b was converted to a cis-α-methylene butyrolactone quantitatively with p-toluenesulfonic acid. Utilization of CpMo(CO) 3 (η 1 -vinylpropargyl) (5) for the synthesis of CpMo(NO)Cl(η 3 -(3R*,4R*)-CH 2 CCHCH-(Me)OC=O) (8) is described; reaction of 8 with RCHO (R = Ph, Me 2 CH) in CH 2 Cl 2 /CH 3 OH gave (1′S*,3R*,4S*)-2-methylene-3-(α-hydroxybenzyl)-4- methylbutyrolactone (9; 52%) and (1′S*,3R*,4S*)-2-methylene-3-(1-hydroxy-2-methylpropyl) butyrolactone (10; 50%), respectively. The stereochemistry of 9 and 10 was elucidated. © 1995 American Chemical Society.