OXYGEN YLIDES-II. PHOTOCHEMICAL AND RHODIUM-CATALYZED REACTIONS OF DIAZOMETHANE WITH (S)-2-METHYLOXETANE
Photolysis of diazomethane in (S)-2-methyloxetane gives 2- and 3-methyltetrahydrofuran (1:3.2), the latter being formed with 21 percent net retention of configuration.In contrast, rhodium acetate catalysis yields racemic 3-methyltetrahydrofuran exclusively.
Kirmse, Wolfgang,Chiem, Pham Van
p. 197 - 200
(2007/10/02)
Access to (S)-2-Methyloxetane and the Precursor (S)-1,3-Butanediol of Hight Enantiomeric Purity
(S)-2-Methyloxetane (1) and its precursor (S)-1,3-butanediol (2) were prepared in low to moderate chemical yield with less than 0.5percent racemization from (S)-ethyl lactate (4) and from (2S,3S)-allothreonine (14b).For the first time the enantiomeric purities of both the starting material and the product (1) were carefully determined by high-precision capillary gas chromatography on optically active resolving stationary phases.The validity of the quadrant rule, correlating the relative configuration of alkyloxiranes with the order of elution from manganese(II) bis (3) by complexation gas chromatography, is also confirmed for 2-methyloxetane (1).
Stereochemistry of Friedel-Crafts Reaction of Benzene with Optically Active 2-Methyloxetane
The Friedel-Crafts alkylation of benzene with (+)-2-methyloxetane in the presence of Lewis acids (AlCl3, SnCl4, and TiCl4) gave 3-phenyl-1-butanol with 20-60percent inversion of configuration at the reaction center and a mixture of 4-chloro-2-butanol and 3-chloro-1-butanol in optically active form as the by-products. These by-products were formed by the attack of the chlorine atom in Lewis acid. The stereochemical course of the reaction to 3-chloro-1-butanol varied with the kind of catalyst, i.e., inversion with AlCl3 or TiCl4 and retention with SnCl4. The addition of nitromethane to the reaction system promoted the retentive ring-opening to 3-chloro-1-butanol.