Hydrotalcite catalysis for the synthesis of new chiral building blocks

<p>The use of hydrotalcites for the synthesis of two chiral building blocks in a simple way is described as a new and green methodology. The synthesis of these compounds implies a regioselective Baeyer–Villiger reaction in a very selective way with ulterior opening and lactonisation. This methodology should be considered green for the use of hydrogen peroxide as the only oxidant and hydrotalcites as the catalyst, and because no residues are produced apart from water. The procedure is very adequate for using in gram scale, in order to increase the value of the obtained compounds. The conditions are excellent and can be applied for nonstable compounds, as they are very mild. The synthesised compounds are magnific starting materials for the synthesis of biologically active or natural compounds. The use of a cheap, commercial and chiral compound as carvone disposable in both enantiomeric forms adds an extra value to this methodology.</p

Diastereoselective synthesis of chiral 1,3-cyclohexadienals

<div><p>A novel approach to the production of chiral 1,3-cyclohexadienals has been developed. The organocatalysed asymmetric reaction of different β-disubstituted-α,β-unsaturated aldehydes with a chiral α,β-unsaturated aldehyde in the presence of a Jørgensen-Hayashi organocatalyst provides easy and stereocontrolled access to the cyclohexadienal backbone. This method allows for the synthesis of potential photoprotective chiral 1,3-cyclohexadienals and extra extended conjugation compounds in a simple manner.</p></div

Synthesis of different chiral cyclohexadienals aromatic and non-aromatic compounds.

<p>Synthesis of different chiral cyclohexadienals aromatic and non-aromatic compounds.</p

General reaction to obtain chiral cyclohexadienals.

<p>General reaction to obtain chiral cyclohexadienals.</p

Experimental optimization of synthesis of chiral cyclohexadienals (4a, 4b) from citral (1) and α,β-unsaturated aldehyde 2.

<p>Experimental optimization of synthesis of chiral cyclohexadienals (4a, 4b) from citral (1) and α,β-unsaturated aldehyde 2.</p

The area of regions UVA (315–400 nm) and UVB (280–315 nm) and molar extinction coefficient of some cyclohexadienals (4a, 20b, 21b, 22b, 23a, 23b) dissolved in <i>i</i>PrOH.

<p>The area of regions UVA (315–400 nm) and UVB (280–315 nm) and molar extinction coefficient of some cyclohexadienals (4a, 20b, 21b, 22b, 23a, 23b) dissolved in <i>i</i>PrOH.</p

UV-Vis absorbance spectra at different λ of 4a, 20b, 21b, 22b, 23a, 23b.

<p>Amplification of the 200–450 nm region and the delimited UVA and UVB regions (ISO-21348).</p

Synthesis of bicycle 12 from cyclohexadienal 4a.

<p>Reagents: a) NaH₂PO₄^.H₂O (2.2 equiv.), NaClO₂ (5%, 2.2 equiv.), 2-methyl-2-butene, <i>t</i>BuOH, r.t., 2h, 99%; b) <i>p</i>-TsOH, MeOH, r.t., 30%.</p

Proposal for the synthesis of new cyclohexadienal building blocks using different catalysts.

<p>Proposal for the synthesis of new cyclohexadienal building blocks using different catalysts.</p

Synthesis of chiral cyclohexadienals (20a-26) from other β-disubstituted-α,β-unsaturated aldehydes (13–19)^a.

<p>Synthesis of chiral cyclohexadienals (20a-26) from other β-disubstituted-α,β-unsaturated aldehydes (13–19)<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192113#t002fn001" target="_blank">^a</a>.</p