Icilio Guareschi and his amazing “1897 reaction”

Abstract

Organic chemistry honors Icilio Guareschi (1847–1918) with three eponymic reactions, the best known ones being the Guareschi synthesis of pyridones and the Guareschi–Lustgarten reaction. A third Guareschi reaction, the so-called “Guareschi 1897 reaction”, is one of the most unusual reactions in organic chemistry, involving the radical-mediated paradoxical aerobic generation of hydrocarbons in near-neutral water solution. A discussion of the mechanism of this amazing reaction, the only metal-free process that generates hydrocarbons, and the implications of the approach in biology and geosciences mirrors the multifaceted scientific personality of the discoverer. Thus, Guareschi’s eclectic range of activities spans a surprising variety of topics, overcoming the boundaries of the traditional partition of chemistry into organic, inorganic, and analytical branches and systematically crosses the divide between pure and applied science as well as between the history of chemistry and the personal contributions to its development.

Scalemic natural products

“…61 The scalemate state of asparagine in leguminous seeds was discovered by Arnaldo Piutti in 1886 in vetches ( Vicia sativa L.) seedlings, and his observation of the distinct taste of the two enantiomers of this amino acid was the first report of different physiological effects associated to a pair of enantiomers. 61,62 In the wake of the studies by Guareschi on asparagine, 63 Piutti crystallized 20 kg of the l -enantiomer from an aqueous extract of 6.5 metric tons of germinated vetches, obtaining then a second crop of crystals from the mother liquors. Much to his surprise, the second crystal crop was a conglomerate of hemihedral crystals, from which, by manual (!!)…”

“…Scheme 13 Oxidative coupling of E-coniferyl alcohol (60) to the furofuran lignan pinoresinol ( 61) is followed by stepwise reduction to lariciresinol (62) and to secoisolariciresinol (63). DP = Dirigent protein, PLR = Pinoresinol-lariciresinol reductases.…”