Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Rearrangements Bayer-Villiger rearrangement

As Table 9.1 shows, for a pressure of 10 bars both the LA conversion and SA selectivity increased with temperature (entries 3-5). On the other hand, at 150°C, the conversion of LA increased with the increase of the pressure while the selectivity to SA registered a constant value (96-98%) (entries 4, 6, and 7). The acidity of the potentially formed and [Ru(H20)j0H] corresponds to strong Bronsted acids (pK = 2.9 at 298 K), that in the presence of hot water seems to be strong enough to catalyze the oxidation reaction by a Bayer-Villiger rearrangement. However, more investigations are necessary to confirm this supposition. [Pg.327]

All reaction steps in Scheme 5.35 are stereoselective. Biocatalytic reduction affords (15,25)-6 with 97.7 % e.e. and 99 % d.e., whereas methylation affords (15, 25)-7 with 90.4 % e.e. The optical purity of (5)-9 on oxidation and Bayer-Villiger rearrangement remains unchanged. [Pg.125]

Oxidation of diphenyl or di-tert. butyl cyclopropenone with wi-chloro peroxy-benzoic acid207 proceeds via intermediates corresponding to a Bayer-Villiger-type mechanism 277/278) to unrearranged products (1,2-diketones) or rearranged products (ketones) depending on the reaction conditions. [Pg.68]

In the past few years, new approaches for the enantioselective synthesis of / -benzyl-y-butyrolactones appeared in the literature. Some of these approaches involve the asymmetric hydrogenation of 2-benzyl-2-butenediols (j [34]), the radical mediated rearrangement of chiral cyclopropanes (r [35]), the transition metal catalyzed asymmetric Bayer-Villiger oxidation of cyclobutanones n [36]), or the enzymatic resolution of racemic succinates (g [37]). [Pg.192]

In principle, reaction of an oxazole, e.g., 15 with 2 could yield triamides 693 and/or 696 via two reasonable pathways (Scheme 1.194). In the first case, path A, [4 + 2] cycloaddition of 02 to 15 would yield an oxazole-2,5-endoperoxide 691. Rearrangement of 691 to an imino-anhydride 692 by a Bayer-Villiger-like reaction and subsequent O-acyl to A/-acyl transfer would produce triamide 693. Alternatively, [2 + 2] cycloaddition of 02 to 15 would produce the dioxetane 694, cleavage of which would then yield a second imino-anhydride 695, which could also undergo an O-acyl to /V-acyl transfer reaction to produce triamide 696. [Pg.152]

The first eiample of an Ireland-Qaisen rearrangement of an allyl lactone employed in natural product synthesis was that of Danishefsky and Tsuzuke in 1980 (Scheme 4.137) [132]. The allyl lactone possessed an exocyclic alkene, and hence resulted in a net 7-membered ring lactone to carbocycle conversion. A Bayer-Villiger reaction converted the pentenoic add to the 3° hydroxyl group of widdrol. [Pg.196]


See other pages where Rearrangements Bayer-Villiger rearrangement is mentioned: [Pg.125]    [Pg.28]    [Pg.47]    [Pg.19]    [Pg.108]    [Pg.263]    [Pg.142]    [Pg.278]    [Pg.173]    [Pg.142]   
See also in sourсe #XX -- [ Pg.650 ]




SEARCH



Bayer

Bayer-Villiger

Bayer-Villiger rearrangement

Villiger

© 2024 chempedia.info