Stereoselective Synthesis of anti‐1,4‐Diols by a BH₃⋅THF‐Mediated Rearrangement of 1,2‐Disubstituted Cyclobutenes

Abstract

A new stereoselective rearrangement of cyclobutylboranes, obtained by the hydroboration of 1,2-disubstituted cyclobutenes, provides anti-1,4-diols with good-to-excellent diastereoselectivity. The mechanism of the rearrangement is discussed based on theoretical calculations.

Investigation of the Impact of Water on the Enantioselectivity Displayed by CALB in the Kinetic Resolution of δ‐Functionalized Alkan‐2‐ol Derivatives

“…The synthesis of the anti-1,4 diol precursors required for rac1b and rac-2b was achieved by the method described by Knapp et al utilizing a diastereoselective BH 3 -mediated rearrangement of 1-substituted 2-methyl-cyclobutenes (Scheme 4). [14] The ring-opening of 3 with BH 3 •THF (1.1 equiv) gave an intermediate borolane, which on treatment with NaOH/H 2 O 2 afforded racemic anti-1,4-diol 4 as the major product in 82% yield with high diastereoselectivity. Compound rac-4 was then converted to rac-1b and rac-2b using 2 or 1 equiv., respectively, of acetic anhydride in an acetylation reaction.…”

Concise Total Synthesis of (+)-Atlanticone C

“…Although no significant byproducts were detected by 1 H NMR analysis of the crude material or could be isolated from the reaction mixture, it is reasonable to assume that hydroboration of the cyclobutene moiety by excess borane occurs and could result in byproducts, leading to decreased yields of 7a and 7b. 20 We attempted to improve the enantiomeric excess of product 7b by repeating the experiment at a lower temperature (entry 3) or at room temperature (entry 4). 21 Although the enantioselectivity of the reduction at -40°C remained high (entry 3), a decrease in selectivity for both diastereomers occurred at room temperature (entry 4).…”

Hydroxy‐Directed, Fluoride‐Catalyzed Epoxide Hydrosilylation for the Synthesis of 1,4‐Diols

“…Therefore, a number of methods have been devised for the synthesis of 1,4‐diols 5. The highest stereoselectivities were obtained for the rearrangement of 1,2‐disubstituted cyclobutenes to anti ‐1,4‐diols,6 the synthesis of syn ‐( E )‐1,4‐diol‐2‐enes using allyl boronates,7 and the preparation of syn ‐ and anti ‐( E )‐1,4‐diol‐2‐enes by a Cu‐catalyzed boration of an allylic epoxide 8…”

“…[4] Therefore,anumber of methods have been devised for the synthesis of 1,4-diols. [5] Theh ighest stereoselectivities were obtained for the rearrangement of 1,2disubstituted cyclobutenes to anti-1,4-diols, [6] the synthesis of syn-(E)-1,4-diol-2-enes using allyl boronates, [7] and the preparation of syn-a nd anti-(E)-1,4-diol-2-enes by aC ucatalyzed boration of an allylic epoxide. [8] Here,w er eport ac omplementary synthetic approach to 1,4-diols that is based on an unprecedented highly regioselective and hydroxy-directed silane reduction of b-hydroxy epoxides.T hermodynamically,e poxide opening through silane reduction is an attractive reaction because ring strain is released and strong C À Ha nd Si À Ob onds are formed.…”