Photochemical Synthesis of β‑N-Heterocycle Alcohols via a Coordination-Induced 1,5-Boronate Sigmatropic Rearrangement

Excited-State Intramolecular Proton Transfer (ESIPT) is an ultrafast nonradiative relaxation pathway that frequently dominates the photophysical fate of conjugated enols, often precluding productive photochemical transformations. Here, we report that bidentate boronate coordination effectively suppresses this process, locking β-N-heterocycle enols into a rigid configuration to enable an efficient photochemical synthesis of β-N-heterocycle alcohols via a 1,5-boronate sigmatropic rearrangement. This strategy circumvents the inherent challenges of hydroxyl acidity and low π-electrophilicity characteristic of the ground-state enol manifold. Operating under mild, metal- and base-free conditions, this protocol facilitates the assembly of 61 diverse aromatic and nonaromatic β-N-heterocycle alcohols (up to 81% yield) using sp ³-, sp ²-, and sp-hybridized organoboronic acids. The methodology exhibits high chemo- and regioselectivityuniquely favoring 1,5-migration to the enol α-carbon over 1,3-addition to the imineand is well-suited for the late-stage functionalization of complex pharmaceuticals. Comprehensive mechanistic studies, integrating picosecond transient absorption (TA) spectroscopy with DFT modeling, identify a discrete excited-state triplet enol as the pivotal intermediate. Crucially, our findings demonstrate that these boronate-enol photochemical transformations proceed via concerted sigmatropic pathways rather than previously assumed photoactivated nucleophilic additions. This work establishes a robust platform for exploiting coordination-induced kinetic control to modulate photochemical outcomes in enol-based substrates.