Tetrahydro-4 H-pyran-4-one: From the Laboratory Scale to Pilot Plant Manufacture
This study describes our recent efforts to find an efficient and scalable route to tetrahydro-4H-pyran-4-one using the commercially available starting materials. The route scouting work and the full development of an efficient access to the target are described. This work culminated in the preparation of above 20 kg of the title compound in our pilot plant facility.
Catalytic SNAr Hydroxylation and Alkoxylation of Aryl Fluorides
Nucleophilic aromatic substitution (SNAr) is a powerful strategy for incorporating a heteroatom into an aromatic ring by displacement of a leaving group with a nucleophile, but this method is limited to electron-deficient arenes. We have now established a reliable method for accessing phenols and phenyl alkyl ethers via catalytic SNAr reactions. The method is applicable to a broad array of electron-rich and neutral aryl fluorides, which are inert under classical SNAr conditions. Although the mechanism of SNAr reactions involving metal arene complexes is hypothesized to involve a stepwise pathway (addition followed by elimination), experimental data that support this hypothesis is still under exploration. Mechanistic studies and DFT calculations suggest either a stepwise or stepwise-like energy profile. Notably, we isolated a rhodium η5-cyclohexadienyl complex intermediate with an sp3-hybridized carbon bearing both a nucleophile and a leaving group.
Prins condensation of formaldehyde with propylene to form 3-buten-1-ol is investigated using microporous solid acid catalysts. Zn/H-beta shows high conversion but leads to a broad product distribution composed primarily of pyrans. Mechanistic studies revealed that 3-buten-1-ol reacts via Prins cyclization or dehydrate to 1,3-butadiene that further reacts with formaldehyde via a hetero-Diels–Alder reaction. These secondary reactions are suppressed over ZSM-5 catalysts: 3-buten-1-ol is the predominant product over H-ZSM-5 zeolite under all conditions investigated. 3-Buten-1-ol selectivity of up to 75 % is achieved. In a second step 3-buten-1-ol dehydrates at temperatures as low as 423 K, forming 1,3-butadiene. Although Br?nsted acid sites are the primary catalytic sites, ion exchange of ZnII increases the overall rate and 3-buten-1-ol selectivity. H-ZSM-5 showed significant differences in reactivity and selectivity as a function of the Si/Al ratio; optimal catalytic properties were observed within Si/Al=40–140.
Vasiliadou, Efterpi S.,Gould, Nicholas S.,Lobo, Raul F.
p. 4417 - 4425
(2017/11/20)
Regioselective Ni(II)-assisted alkylation of 2-methoxy-5,6- dihydro-2H-pyran: A new route to 2-n.alkyl-5,6-dihydro-2H-pyrans
In the presence of a catalytic amount of NidppeCl2, 2-methoxy- 5,6-dihydro-2H-pyran reacts with primary Grignard reagents to give the corresponding 2-n.alkyl-5,6-dihydro-2H-pyrans in satisfactory yields.