Oxygen-Directed Intramolecular Hydroboration

Abstract

Metal-free homoallylic oxygen-directed intramolecular hydroboration is reported. Regioselectivities from 20:1 to 82:1 favoring the 1,3-dioxy-substituted products have been achieved using Me2S·BH3/TfOH followed by standard oxidative workup. Branching at the C5 position improves regioselectivity.

A Versatile Bis‐Allylboron Reagent for the Stereoselective Synthesis of Chiral Diols

“…The complementary silylation pattern ( 6 ) is accessible from 2 j after treatment with one equivalent of tert ‐butyl dimethylsilyl chloride (TBSCl) . Another example in which the pendant allylboronate group of 3 serves as a masked allylic alcohol is the selective hydroboration reaction of the terminal double bond leading to triol 7 after oxidative workup, which was not feasible starting from 2 j . Moreover, the allyl boronate group in 3 could be activated as the ate complex with chloromethyl lithium to undergo Matteson homologation, yielding 1,6‐diol 8 .…”

“…After oxidative workup,t he 1,5-diols 2a-m were obtained with good yields and enantioselectivities (Table 1). [34] Moreover,t he allyl boronate group in 3 could be activated as the ate complex with chloromethyl lithium to undergo Matteson homologation, yielding 1,6-diol 8. !…”

“…[33] Another example in which the pendant allylboronate group of 3 serves as am asked allylic alcohol is the selective hydroboration reaction of the terminal double bond leading to triol 7 after oxidative workup,w hich was not feasible starting from 2j. [34] Moreover,t he allyl boronate group in 3 could be activated as the ate complex with chloromethyl lithium to undergo Matteson homologation, yielding 1,6-diol 8. [35,36] In this instance,b oric ester 3 acts as an in situ protecting group for the secondary hydroxy group.…”

Direct Access to Monoprotected Homoallylic 1,2-Diols via Dual Chromium/Photoredox Catalysis

“…[2,11,12] This provides selective access to both the syn and the anti product. Secondly, the allyl moiety can serve as a synthetic linchpin, enabling a variety of subsequent established transformations, such as dihydroxylation, [13] epoxidation, [14] ozonolysis, [15] hydroboration [6,7,16] and many more [9,17] (Figure 1A). While there are important reports to access this motif either via a n-BuLi initiated siloxy- [2,3] Wittig rearrangement [18] or the addition of acetals to aldehydes, [19] these methods were developed specifically for one type of protecting group and therefore lack generality.…”

Ein vielseitiges Bisallylbor‐Reagenz für die stereoselektive Synthese von chiralen Diolen

“…[33] Another example in which the pendant allylboronate group of 3 serves a masked allylic alcohol is the selective hydroboration reaction of the terminal double bond leading to triol 7 after oxidative workup, which was not feasible starting from 2j. [34] Moreover, the allyl boronate group in 3 could be activated as the ate complex with chloromethyl lithium to undergo Matteson homologation, yielding 1,6-diol 8. [35,36] In this instance, boric ester 3 acts as an in-situ protecting group for the secondary hydroxy group.…”