Asymmetric Catalysis by Vitamin B₁₂. The isomerization of achiral epoxides to optically active allylic alcohols

Abstract

Achiral epoxides are isomerized to optically active allylic alcohols under the influence of catalytical amounts of cob(1)alamin in protic polar solvents.Introduction. -The isomerization of epoxides to allylic alcohols is an important transformation in organic synthesis and an industrial process [l] Enantioselective isomerization of achiral epoxides to optically active allylic alcohols with chiral lithium amides (from BuLi and enantiomerically pure secondary amines) has recently been described by Whitesell and Felman [17] and Asami [18]. The yield and enantiomeric excess strongly depend on the epoxide, the base, and the solvent.Continuing our investigations on the application of vitamin B,, [19] as catalyst in organic synthesis [20], we report here on preliminary results on the B,,-catalyzed isomerization of achiral epoxides to optically active allylic alcohols. This work was stimulated to a considerable extent by earlier findings of Fischli et al. on the cob(1)alamin-catalyzed enantioselective hydrogenation of Michael-olefins [2 11 and the work of Golding and coworkers on the stereochemistry of the alkylation of cob(1)alamin by racemic epoxides [221.Results and Discussion. ~ If achiral epoxides like la, b, d are dissolved in a polar protic solvent containing a catalytic amount of vitamin B,,, [23], the corresponding optically active allylic alcohols 2a, b, dare formed on standing at room temperature (Scheme). The

Asymmetric Catalysis by Vitamin B12: The isomerization of achiral cyclopropanes to optically active olefins

“…Since sec-alkylcob(I1I)alamins easily undergo dehydrocobaltation to olefins, H', and cob(I)alamin, we became interested in the reaction of cob (1) (6) and C(7), respectively. As an extension of our previous work on the enantioselective isomerization of epoxides to allylic alcohols [9] and aziridines to allylic amines [lo], we report here on the cob(1)alamin-catalyzed conversion of the achiral spiroactivated cyclopropanes 1 to the optically active (R)-(cycloalk-2-enyl)-Me~drum's acids 2 (Scheme I ) . I) Cob(I)alamin-Catalyzed Isomerization.…”

“…139 (lo), 138 (52), 137 (27), 135 (29), 134(61), 133(7), 132(11), 123(15), 113(5), I l l (7), 110 (8), 108(9), 107(43), 106(44), 105(18), 101 (10),99(4), 97 (5), 95 (7), 94 (4), 93 (28), 92 (6), 91 (6), 81 (8),80 (16),79 (IOO),78 (25),77 (44),75 (4). 71 (5), 69 (lo), 68 (lo), 67 (41), 66 (16), 65 (7), 59 (37), 55 (9), 54 (5), 53 (16), 52 (1 l), 51 (9), 50 (4), 45 (6), 44 (4), 41 (19), 40 (4), 39 (19), 29 (7), 28(15),27 (8), 18(17), 17(7), 14(19).…”

Enantioselective Catalysis with Chiral Cobalt and Copper Complexes

“…B12-CATALYZED ISOMERIZATION OF EPOXIDES (cf. Scheme17) (56) General Procedure(561. Cyclopentene Oxide -7 {+)-2-Cyclopentene-1-01.…”

Organic Reactions in the Solid State: The reactivity of guest molecules in tri‐o‐thymotide clathrates

“…Depending on the substrate, either one of two paths were then observed: addition of the hydrogen halide to the double bond to form a halohydrin (Step B ) or nucleophilic substitution of the OH group leading to an CQ -unsaturated halide (Step C). By way of contrast, in solution, strongly basic reagents [7], Lewis acids [8], or vitamin B,, in catalytic amounts [9] led to allylic alcohols. Isomerization by heterogeneous catalysis with solid acids or bases also proved to be practicable [lo].…”