Abstract
Protection techniques of functional groups within the structure of organic compounds are important synthetic methods against unwanted attacks from various reagents during synthetic sequences. Acetal and thioacetal groups are well known as protective functional groups in organic reactions. In this study, acetalization of carbonyl compounds with diols and dithiols and methoxymethylation of alcohols with formaldehyde dimethyl acetal (FDMA) have been carried out using sulfamic acid-functionalized magnetic Fe3O4 nanoparticles (SA-MNPs) as a heterogeneous solid acid catalyst. Products were characterized by FT-IR and NMR spectroscopies. The structural and electronic properties of some products were computed by quantum mechanical (QM) methods. Depending on the stereochemistry and electronic properties that were obtained by computational results, we have suggested that hyperconjugation plays a key role in the structural properties of 2-phenyl-1,3-dioxolane derivatives, and also the electron transfer between π-electrons of the aromatic ring with the 3d orbital of S-atoms influences the 2-phenyl-1,3-dithiane derivatives' structure.
Highlights
Protection strategies of carbonyl compounds are well known as one of the most important branches of organic chemistry in the eld of multistep total synthesis of enantiomerically pure natural and non-natural compounds.[1]
To compare the efficiency of sulfamic acid-functionalized magnetic Fe3O4 nanoparticles (SA-MNPs) catalyst for acetalization reaction, different organic and inorganic solid acid catalysts were examined upon the reaction of 4-nitrobenzaldehyde (0.151 g, 1 mmol) with ethylene glycol (0.11 mL, 2 mmol) (Table 1)
Trityl chloride and trityl bromide were examined as solid acids for described reaction and the desired product was obtained in 76% yield
Summary
Protection strategies of carbonyl compounds are well known as one of the most important branches of organic chemistry in the eld of multistep total synthesis of enantiomerically pure natural and non-natural compounds.[1] For example, protection strategies were applied in the synthetic processes of (À)-dihydroa atoxin D2,2 (À)- & (+)-microminutinin,[2] optically active vitamin E3 and bryostatin 1 Several methods have been reported for protection of alcohols with formaldehyde dimethoxy acetal (FDMA).[22] The trace and impact of anomeric effect can be observed in methoxymethylation of alcohols. Due to the interaction between two-electrons of the lower energy orbital (s-bond or a lone pair) with the higher energy empty antibonding orbital, has made a stabilized molecule by hyperconjugation concept (Fig. 3).24a. Scheme 2 Chemoselective methoxymethylation of benzylic alcohols and its hydrolysis process
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