Envision a system of millions of forming and destructive chemical reactions. Now, envision that intermediates of there reactions associate through non-covalent means and that this complex becomes protected against the destructive reactive pathway, perhaps by a reversible precipitation. These new complexes result in a localized increased of new chemical species. These chemical species then progress in a new series of reaction... that is what I mean through cooperative means. I acknowledge this is complete speculation, but well within the range of chemical possibility. As long as there was enough free energy for these reaction to occur.
Consider combustion chemistry. It's an oxidative process which predominately oxidizes fuels into smaller MW products, CO and CO2. Yet, larger mw products can and typically do form during this process due to the excess energy present. And during the mapping of it's pathways, intermediates have been shown to combine to form new compounds. Granted these are transient and thermodynamically unstable, but highlight the shear complexity of something as benignly simple as burning. If you wish to know more, look into Phil Westmoreland and combustion.