Diastereo‐ and Enantiomerically Pure Allylboronates: Their Synthesis and Scope

Abstract

Allylboronates are highly attractive reagents for allyl additions. Enantiomerically pure, stable reagents with a stereogenic centre in alpha-position to boron are especially versatile, albeit often difficult to synthesize. Starting from boron-containing allyl alcohols 6 and 7, which are discussed in detail herein, a set of reagents were obtained via [3,3]-sigmatropic rearrangements and consecutive transformations in the side chain. The configurations could be established first by chemical correlation, but also by X-ray crystallography (16, 18, 34, and 39). Allyl additions were performed resulting in the formation of predominantly (Z)-configured homoallylic alcohols (31, 43-45) with high enantiomeric excess. Detailed investigations on the matched-mismatched interaction between the reagents 15/16 (and ent-15/ent-16, respectively) and isopropylidene glyceraldehyde 42d are presented.

Importance of the Support Properties for Immobilization or Purification of Enzymes

“…For convenience during the work‐up procedure, the crude products were directly reduced with LiAlH 4 to give the corresponding diols (i.e., 15 and 16 , from 13 and 14 , respectively). The overall yields were moderate (31–65 %), but the enantioselectivity was relatively low compared to that obtained with unsubstituted reagents 4 and 5 (Scheme , R 1 = H) 5a,5d. In contrast to this moderate enantioselectivity, the allyl addition showed complete ( Z ) selectivity (>95 % as detected by NMR spectroscopy), which can be attributed to the pseudo‐axial position of the α substituent in transition states TSA and TSB .…”

Total Synthesis of Solandelactones A and B

“…Based on our detailed studies of the preparation, derivatization and application of diastereomerically pure α‐substituted allylboronic esters,11 the structural motif of cis ‐configured homoallylic alcohols was envisioned to call for extension of the methodology to provide an efficient route to desired compound 2 as well as its enantiomer ent ‐ 2 . Starting from diastereomerically pure mesylates 6 and dia ‐ 6 ,12,11b allylation reagents 4 and dia ‐ 4 were obtained by a copper‐mediated substitution reaction with n ‐propylmagnesium bromide (Scheme ). With these reagents in hand, two alternative routes to vinyl iodide 2 via allylation reactions were developed.…”

Modelling Binuclear Metallobiosites: Insights from Pyrazole‐Supported Biomimetic and Bioinspired Complexes

“…More recently, another elegant diastereoselective method was also reported based on a copper‐catalyzed addition of bis(pinacolato)diboron to N ‐ tert ‐butanesulfinyl aldimines 4b. Other approaches are more limited in terms of generality by the nature of the starting products, such as borylation of organometallic compounds,4c S N 2′ reactions,4d,e electrophilic amination4f or [3,3]‐sigmatropic rearrangements 4g…”