10035-98-0Relevant academic research and scientific papers
Diradical-promoted two-carbon ring-expansion reactions by thermal isomerization: Synthesis of functionalized macrocyclic ketones
Rueedi, Georg,Hansen, Hans-Juergen
, p. 1628 - 1665 (2007/10/03)
A new method for the smooth and highly efficient preparation of functionalized macrocyclic ketones has been developed. Pyrolysis of medium- and large-ring 3-vinylcycloalkanones by dynamic gas-phase thermo-isomerization (DGPTI) at 600-630° yielded, under insertion of a previously attached vinyl side chain by means of a 1,3-C shift, the corresponding γ,δ- unsaturated cycloalkanones. The yield of the two-carbon ring-expanded ketones greatly depended on the relative ring strains of substrate and product (5-87%, cf. Table 5). The formation of minor amounts of one-carbon ring-expanded cycloalkenes (10%) can be ascribed to a subsequent decarbonylation step. A reaction mechanism involving initial cleavage of the weakest single bond in the molecule has been established (cf. Scheme 6). Recombination within the generated diradical intermediate in terminal vinylogous position led to the observed products, while reclosure gave recovered starting material. Substituents on the vinyl moiety were transferred locospecifically into the ring-expanded products. An isopropenyl group did not significantly affect the isomerization process, whereas substrates bearing a prop-1-enyl group in β-position enabled competing intramolecular H-abstraction reactions, leading to acyclic dienones (cf. Schemes 9-11). DGPTI of the 13-membered analogue directly yielded 4-muscenone, which, upon hydrogenation, led to the valuable musk odorant (±)-muscone. Increasing the steric hindrance on the vinyl moiety gave rise to diminishing amounts of the desired γ,δ-unsaturated cycloalkanones. This novel two-carbon ring-expansion protocol was also successfully applied to 3-ethynylcycloalkanones, giving rise to the corresponding ring-expanded cyclic allenes (cf. Scheme 13).
Iodine(V) reagents in organic synthesis. Part 4. o-Iodoxybenzoic acid as a chemospecific tool for single electron transfer-based oxidation processes
Nicolaou,Montagnon,Baran,Zhong
, p. 2245 - 2258 (2007/10/03)
o-Iodoxybenzoic acid (IBX), a readily available hypervalent iodine(V) reagent, was found to be highly effective in carrying out oxidations adjacent to carbonyl functionalities (to form α, β-unsaturated carbonyl compounds) and at benzylic and related carbon centers (to form conjugated aromatic carbonyl systems). Mechanistic investigations led to the conclusion that these new reactions are initiated by single electron transfer (SET) from the substrate to IBX to form a radical cation which reacts further to give the final products. Fine-tuning of the reaction conditions allowed remarkably selective transformations within multifunctional substrates, elevating the status of this reagent to that of a highly useful and chemoselective oxidant.
Recoverable chiral sulfoxides for asymmetric synthesis: application to stereoselective carbonyl reduction and the asymmetric synthesis of allylic alcohols
Butlin, Roger J.,Linney, Ian D.,Mahon, Mary F.,Tye, Heather,Wills, Martin
, p. 95 - 106 (2007/10/03)
The enantiomerically pure cyclic sulfinamide S(S)R-(+)-3 reacts with the sodium enolates of ketones to give the corresponding homochiral sulfoxides.Reduction of the carbonyl group in these products may be achieved using a variety of reducing agents the best of which were DIBAL-H or DIBAL-H/ZnBr2, which give complementary products of high diastereomeric excess.Reduction of the hydroxy sulfoxides with Raney nickel proceeds in low yield and causes partial racemisation of the products.However the combined use of a durected reduction followed by a facile sulfenic acid elimination provides a synthesis of allylic alcohols in high enentiomeric excess.
