Scheme 1.

a) Addition of sulfonyl halides to BCBs. b) Giese reaction of a sulfonyl BCP iodide. c) Synthesis and functionalization of phosphonate BCP bromides (see the Supporting Information for detailed reaction conditions). [a] Reactions carried out on a 0.1 mmol scale according to the title scheme, using 2.5 equiv of 2  a (1.0 M in H₂O) and either 1.4 equiv of BnNMe₃ICl₂ or 1.8 equiv of Br₂, stirred for 2 min before addition of 1.0 equiv of BCB 9 (0.1 M in CH₂Cl₂) and 10 mol % Et₃B. [b] The major diastereoisomer of 10  b‐I was assigned by NOESY correlations; other adducts were assigned by comparison of ¹H NMR spectra. [c] 2.5 mol % Ir[(dF(CF₃)ppy)₂(dtbbpy)]PF₆, 2.0 equiv of Na₂CO₃, 2.0 equiv of (Me₃Si)₃SiH, 6.0 equiv, of dehydroalanine, MeOH/H₂O (1 : 1), blue LEDs, rt, 18 h. [d] 2.5 equiv of 2  a (1.0 M in H₂O) and 1.4 equiv of BnNMe₃ICl₂ in CH₂Cl₂ were pre‐stirred at 0 °C for 2 min, then added to a vial containing reagents as in [c] and 1.0 equiv of 1; (Me₃Si)₃SiH was added last. Structure of 10  d‐I and 11 from X‐ray diffraction studies, displacement ellipsoids are drawn at 50 % probability, hydrogen atoms and disordered solvent (11 only) are omitted for clarity. ^[14] Boc=tert‐butoxycarbonyl. DPPA=diphenylphosphoryl azide.