Stereoselective synthesis of alcohols, XXXI: Stereoselective CC bond formation using chiral Z‐pentenylboronates

Abstract

Homoallyl alcoholsUsing 1,2-dicyclohexyl-1,2-ethanediol as chiral auxiliary, the enantiomerically pure 2-pentenylboronate 9c was obtained. Its addition to benzaldehyde proceeded with complete transfer of chirality to give the syn-E-homoallyl alcohol 11. The ability of the reagent 9c to create new stereocenters under reagent control of diastereoselectivity was tested in its addition to the chiral aldehydes 15 and 24. This resulted in a short and stereospecific synthesis of invictolide (18), as well as of a C-9/C-15-partial structure 25 of erythronolide A.One strategy for the synthesis of natural products of polyketide-derived biogenesis, especially for the synthesis of polypropionate molecules2), consists in an iterative sequence of chain elongation steps.Stereoselektive Syntbese von Alkoholen, XXXI'? -Stereosdektive C-C-Bindungsbildung mit Hilfe chirakr Z-Pentenylboro&4uter Unter Verwendung von 1,2-Dicyclohexyl-l,2-ethandiol als chiralem Auxiliar wurde der enantiomerenreine Z-Pentenylboronsaureester 9c erhalten. Dessen Addition an Benzaldehyd ergab den syn-E-Homoallylalkohol 11 unter vollstandiger ChiralitatsObertragung. Die Fihigkeit des Reagenz 9c zur Bildung neuer Stereozentren unter Reagenz-Kontrolle der Diastereoselektivitat wurde in der Addition an die chiralen Aldehyde 15 und 24 gepruft. Dies fiihrte zu einer kurzen stereospezifischen Synthese des Invictolids (18) wie der eines C-9/C-15-Bausteins 25 des Erythronolids A.Control of the formation of the individual stereocenters depends on simple diastereoselection during the carboncarbon bond forming steps3) as well as on reagent control of diastereo~electivity~) using chiral reagents exerting high asymmetric induction. We recently reported on cr-methoxy-(E)-crotylboronates (1) as reagents, which allow for the generation of the stereotriades C and D'). Here, we would like to describe the chiral 2-pentenylboronate 2, which should allow for the generation of the stereotriades A and B. Some aspects of this work have already been communicated in preliminary form ' 1.A preceding study on racemic E-and Z-pentenylboronates') demonstrated that only the Z isomer 3 shows high diastereoselectivity on addition to aldehydes. The product 4 with an E-double bond is formed preferentially since the transition state 5 of the competing reaction leading to 6 with a 2-double bond is destabilized by allylic 1,3-strain6). As the Chem.

Pheromone of the elm bark beetle Scolytus laevis (Coleoptera: Scolytidae): stereoisomers of 4-methyl-3-heptanol reduce interspecific competition

“…However, preparations of (1S,2S)-1,2-diisopropyl-1,2-ethanediol and its enantiomer are laborious, and in the present synthesis we instead used the similarly C 2 -symmetrical 1,2-dicyclohexyl-1,2-ethanediol esters. These also induce very high stereoselectivity (Hoffmann et al 1989), and the diol is easily prepared (Hiscox and Matteson 1996). Its utility for asymmetric syntheses has been demonstrated repeatedly (for example, Matteson and Man 1994;Matteson et al 1998;Man et al 1999).…”

“…The syntheses of all four stereoisomers of 4-methyl-3-heptanol from (R,R)-and (S,S)-1,2-dicyclohexyl-1,2-ethanediol boronic esters proceeded smoothly. Although diastereomeric purities were not scrutinized as rigorously as those reported previously (99.5-99.8%, Tripathy and Matteson 1990), there was no evidence of any diastereomeric cross contamination in the 13 C NMR spectra of intermediates or final products, and there is evidence that 1,2-dicyclohexyl-1,2-ethanediol boronic esters provide diastereoselectivity as high or higher than the 1,2-diisopropyl-1,2-ethanediol analogs (Hoffmann et al 1989). Accordingly, both enantiomeric and diastereomeric impurities were presumably very low, \1%, too small to detect by routine methods.…”

Recent Advances in the Preparation of Allylboronates and Their Use in Tandem Reactions with Carbonyl Compounds

“…However, the low reactivity of many alkenylmetal species can sometimes bring about poor yields in the alkylation. While the reactions of alkenyllithium [34][35][36] and alkenylmagnesium [33] reagents with halomethaneboronates are well established, the high reactivity of these organometallics limits the type of functional groups that may be present. In this regard, less reactive alkenylaluminum [37,38] (Equation 7) and alkenylcopper [39,40] reagents (Equation 8) have been used to produce more sensitive, functionalized allylboronates such as the 2-carboxyester allylboronates 13 and 17 from alkyne precursors.…”

“…For example, condensation between bisallylic alcohol 66 and allylboronate 59 provided the corresponding mixed boronic ester, which was treated with chiral catalyst 67 to give optically pure cyclic allylboronate 68 (Equation 36). The corresponding diol was isolated after oxidation of 68.…”

“…In transition structure B, unfavorable steric interactions between the pseudo-equatorial chloro substituent and the dioxaborolane substituents are unavoidable. The authors had previously shown that the DICHED auxiliary had no effect on the stereochemical outcome of the reaction [36]. Thus, the α-chloro center and not the chiral boronate unit is the main contributor to the highly efficient transfer of chirality in these allylations.…”