Chain Extension of Boronic Esters with Lithiooxiranes Generated by Sulfoxide–Metal Exchange – Stereocontrolled Access to 2°/2°, 2°/3°, and 3°/3° Vicinal Diols and Related Compounds

Abstract

AbstractLithiooxiranes [LiCR1(O)CR2R3, R1 = H, Me; R2/R3 = H/Ph, H/tBu, Me/Ph], generated by sulfoxide–lithium exchange from stereodefined sulfinyl epoxides (with use of PhLi or tBuLi, THF, at or below –90 °C), were employed for the stereospecific reagent‐controlled homologation of boronic esters R0–Bpin (R0 = BnCH2, allyl, cHex, Ph). Addition of TBSOTf to the intermediate ate complexes gave β‐silyloxyboronates that were converted to vicinal diol monosilyl ethers by oxidative work‐up with aq. NaOOH. The 2°/2° (4–32 %, dr > 98:2), 2°/3° (21–66 %, dr ≥ 65:35), and 3°/3° (59–68 %, dr ≥ 95:5) contiguous stereodiad‐containing compounds created in this manner were typically obtained in a highly stereocontrolled manner. In general, cis‐sulfinyl epoxides afforded anti‐like stereodiads, whereas trans‐sulfinyl epoxides afforded syn‐like stereodiads; however, as a result of its suspected configurational instability, LiCMe(O)CHPh gave anti‐like 2°/3° motifs regardless of sulfinyl epoxide stereochemistry.