Gas-Phase Sugar Formation Using Hydroxymethylene as ......André K. Eckhardt, Michael M. Linden,...

André K. Eckhardt, Michael M. Linden, Raffael C. Wende, Bastian Bernhardt, and Peter R. Schreiner*

Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, D-35392 Giessen,E-Mail: Andre.K.Eckhardt@org.chemie.uni-giessen.de

Gas-Phase Sugar Formation Using Hydroxymethylene as the Reactive Formaldehyde Isomer

Literature[1] Butlerow, A. Ann. Chem. Pharm. 1861, 120, 295-298. [2] Hollis, J. M., Lovas, F. J., Jewell, P. R. Astrophys. J. 2000, 540, L107-L110; Halfen, D. T., Apponi, A. J., Woolf, N., Polt, R., Ziurys, L. M. Astrophys. J. 2006, 639, 237-245. [3] Schreiner, P. R., Reisenauer, H. P., Pickard IV, F. C., Simmonett, A. C., Allen, W. D., Matyus, E., Csaszar, A. G. Nature 2008, 453, 906-909; Schreiner, P. R. J. Am. Chem. Soc. 2017, 139, 15276-15283. [5] Breslow, R. Tetrahedron Lett. 1959, 1, 22-26. [6] Eckhardt, A. K.; Linden, M. M.; Wende, R. C.; Bernhardt, B.; Schreiner, P. R. Nature Chem. 2018, 10, 1141-1147.

Introduction & Motivation

The mechanism for the uncatalyzed dimerization of two formaldehyde (2a)molecules to glycolaldehyde (1a) and further to higher sugars is a riddle to date(Scheme 1).[1] While 1a has been detected in interstellar media[2] we preparedsimple sugars in iterative gas phase formose-type reactions under interstellarconditions via highly reactive hydroxymethylene[3] as Breslow’s[4] ‘activeformaldehyde’ isomer.

Results & Discussion

We performed two types of experiments, namely quantitative flow pyrolysis(FP) combined with standard 1H and 13C NMR analysis as well as high-vacuumflash pyrolysis (HVFP) experiments coupled with matrix isolation IRspectroscopy in solid argon at cryogenic temperatures.[5] High-level coupledcluster ab initio computations confirm our proposed nearly barrierless ‘carbonylene’ reaction mechanism and experimental results.

Scheme 1 | Mechanistic hypotheses related to sugar formation from formaldehyde.

Figure 3 | 1H NMR spectra of products resulting from the FP of glyoxylic acid (4a).

Figure 4 | Computed potential energy surface for the formation ofglycolaldehyde via hydroxymethylene and formaldehyde. The ‘carbonyl ene‘reaction is nearly barrierless.

Figure 2 | Reaction of methylhydroxycarbene (3b), generated by high-vacuumflash pyrolysis (HVFP) of pyruvic acid (4b), with formaldehyde (2a) tohydroxyacetone (1c) via a barrierless ‘carbonyl ene‘ reaction at cryogenictemperatures under matrix isolation conditions in solid argon. The C–Hinsertion product lactaldehyde (1b) was experimentally not observed.

Figure 1 | Home-build flow pyrolysis (FP) apparatus (top left) and cryogenicmatrix isolation apparatus (bottom right).

Conclusions & Outlook

The simplest aldoses, glycolaldehyde and glyceraldehyde, can form directly via anessentially barrierless iterative ‘carbonyl ene‘reaction of hydroxymethylene withthe corresponding aldehyde. This is an alternativeconcept for interstellar glycolaldehyde andsubsequent sugar formation.