Diones, molecular rearrangement

In addition, other work showed that 3-hydroxy-4,5-dimethyl-2(5H)-furanone can be formed thanks to a Maillard reaction of hexoses and pentoses in the presence of cysteine 20). Due to the non-linear structure of Sotolon, its formation cannot simply be explained directly from sugar cyclization during tire Maillard reaction, like other furanones such as Furaneol. Hence, it is likely tliat Sotolon results from rearrangement of Amadori products of low molecular weight like butan-2,3-dione (diacetyl) and hydroxyacetaldehyde, via an aldol condensation (Figure 6). 

An outstanding example of a branching pathway exploited complementary cyclisation reactions to yield alternative molecular scaffolds (Scheme 1.5). A four-component Petasis condensation reaction was used to assemble flexible cyclisation precursors e.g. 14). Alternative cyclisation reactions were then used to yield products with distinct molecular scaffolds Pd-catalysed cyclisation (- 15a) enyne metathesis (- 15b) Ru-catalysed cycloheptatriene formation (- 15c) Au-catalysed cyclisation of the alcohol onto the alkyne (- 15d) base-induced cyclisation (- 15e) Pauson-Khand reaction 15f) and Miesenheimer [ 2,3]-sigmatropic rearrangement (not shown). Four of these cyclisation reactions could be used again to convert the enyne 15e into molecules with four further scaffolds (17a-d). In addition, Diels Alder reactions with 4-methyl-l,2,4-triazoline-3,5-dione converted the dienes 15b, 17a and 17d... 

---