The synthesis of saturated N-heterocycles remains of utmost importance and an industrially relevant field where improvement and development of more facile methods for accessing these scaffolds is paramount. With this work, we have expanded the biocatalytic reaction toolbox through the demonstration of novel IRED catalysed annulation reactions and have demonstrated how enzyme engineering may influence catalysis with the first alcohol oxidase capable of generating di-aldehydes with complete chemoselectivity. Through applying these enzymes in combination, four distinct synthetic steps were achieved within one pot and transformations previously unique to heavy metal catalysed borrowing hydrogen chemistry requiring forcing conditions are achieved at 30 °C in water, with an expanded amine scope. The ability to form α-substituted heterocycles is a transformation underrepresented in borrowing hydrogen catalysis, and here we demonstrate it with stereocontrol, culminating in a simplified route to the valuable natural product (S)-nicotine. Finally, by extending this work to the synthesis of N-alkylated α,α-disubstituted pyrrolidines from simple diketone starting materials, we have demonstrated a remarkable ability of these biocatalysts to build complexity with complete diastereomeric control. While there are limits to the synthetic application of our methodology, the recent expansion of our imine reductase panel demonstrated in the diketone cascade and the potential for the engineering of these enzymes towards this chemistry presents enormous potential. With the unprecedented speed that IREDs have moved from discovery to industrial application, we are hopeful that this novel methodology may achieve a similar impact.