Organoboranes. 52. The successful ring enlargement of boracyclanes via sequential one‐carbon homologation: The first synthesis of boracyclanes in the strained medium‐ring range

Previous attempts to synthesize boracyclanes in the medium‐ring range (9‐, 10‐, 11‐, and 12‐ring members) via cyclic hydroboration of α,ω‐dienes have failed. However, their synthesis via the sequential one‐carbon homologation of B‐methoxyboracyclanes has been achieved utilizing the successive reaction of B‐methoxyboracyclanes with in situ generated (chloromethyl)lithium (LiCH2Cl): MeOB(CH2)5 → MeOB(CH2)6 → MeOB(CH2)7 → MeOB(CH2)8 → MeOB(CH2)9 → MeOB(CH2)10 → MeOB(CH2)11. The yields achieved are in the range of 75–85%. In each case the products are identified by conversion via the DCME reaction into the known cycloalkanones. This development provides the first entry into boracyclanes of the strained medium ring range.