From intermediate 3 2E-anti, the ring-closing step was explored. First, the anti and syn isomers were found to be very close in energy (0.6 kcal/mol). Interestingly, the ring closing transition states in the triplet state for both isomers were prohibitively high in energy (>30 kcal/mol) due to the loss of conjugation in the diradical system, forming a 90º C-C single bond and losing the stereochemical information of the double bond, that would result in a cis-trans mixture of both anti and syn products. However, a Minimum Energy Crossing Point (MECP) was located, using the easyMECP software, for both the anti and the syn isomers before the triplet transition states at 2.39 Å of the C-C bond formation. In both cases, once the triplet→singlet ground state transition occurs at a conical intersection, the singlet state proceeds thermodynamically downhill to products 1 E-Prodanti and 1 E-Prodsyn via radical recombination. Again, the higher stability of the MECPanti, due to the reduced steric hindrance, compared to the MECPsyn, 3.0 kcal/mol, aligns with the experimentally observed diastereoselectivity. Due to the higher excited state energy of the shorter styrene chromophore, reexcitation of the formed (E)-isomer via EnT is inefficient as supported by control experiments (See ESI for full details). In a bid to demonstrate the power of the developed method, geminal BPin products 18 and 35 were further derivatized (Scheme 5). Oxidation of 18 resulted in a subsequent Bayer-Villiger reaction to afford lactone 44 in high yield, while oxidation of 35 generated bicyclic ketone 45. Base-mediated protodeboronation, furnished syn diastereomers 46 and 47 in high yields providing a complimentary approach to the opposite diastereomer generated under EnT catalysis (Scheme 1).