((TRITYLOXY)METHYL)BORONIC ESTERS

Sodium trityl oxide with omomethyl)-4,4,5,5-tetramethyl-1,3,2-dioxabor olane [pinacol (bromomethyl)boronate (1)] in dimethyl sulfoxide effici ently yields l-2-[(triphenylmethoxy)methyl]-1,3,2-dioxaborolane (3), w hich can be transesterified with chiral diols to form other [(tripheny lmethoxy)methyl]-1,3,2-dioxaborolanes. These can undergo chain extensi on with (dichloromethyl)lithium in the normal manner and are potential ly useful synthetic intermediates. The majority of known boronic ester s are liquids, but the trityl group confers crystallinity on several e xamples. Six structures have been determined: l-2-[(triphenylmethoxy)m ethyl]-1,3,2-dioxaborolane (3), [R-(4 alpha,5 ta)]-4,5-dicyclohexyl-2- [(triphenylmethoxy)methyl] (4), [S-(4 alpha,5 )-2-[(triphenylmethoxy)m ethyl]-1,3,2-dioxaborolane (5), (R)-pinanediol ((trityloxy)methyl)boro nate (ent-6), (S)-pinanediol (S)-(1-chloro-2-(trityloxy)ethyl)boronate (7a), and (S)-pinanediol (S)-(1-bromo-2-(trityloxy)ethyl)boronate (7b ). The 1,3,2-dioxaborolane ring is very nearly planar, consistent with strong oxygen-boron pi-bonding.