91796-48-4Relevant academic research and scientific papers
Diastereoselective nucleophilic substitution reactions of oxasilacyclopentane acetals: Application of the "inside attack" model for reactions of five-membered ring oxocarbenium ions
Bear, Teresa J.,Shaw, Jared T.,Woerpel
, p. 2056 - 2064 (2002)
The additions of nucleophiles to oxocarbenium ions derived from oxasilacyclopentane acetates proceeded with high diastereoselectivity in most cases. Sterically demanding nucleophiles such as the silyl enol ether of diethyl ketone add to the face opposite the C-2 substituent. These reactions establish the syn stereochemistry about the newly formed carbon-carbon bond. Small nucleophiles such as allyltrimethylsilane do not show this same stereochemical preference: they add from the same face as the substituent in C-2-substituted oxocarbenium ions. The stereoselectivities exhibited by both small and large nucleophiles can be understood by application of the "inside attack" model for five-membered ring oxocarbenium ions developed previously for tetrahydrofuran-derived cations. This stereoelectronic model requires attack of the nucleophile from the face of the cation that provides the products in their lower energy staggered conformations. Small nucleophiles add to the "inside" of the lower energy ground-state conformer of the oxocarbenium ion. In contrast sterically demanding nucleophiles add to the inside of the envelope conformer where approach is anti to the C-2 substituent of the oxocarbenium ion, regardless of the ground-state conformer population.
Synthetic studies on a marine natural product, palmerolide A: Synthesis of C1-C9 and C15-C21 fragments
Kaliappan, Krishna P.,Gowrisankar, Parthasarathy
, p. 1537 - 1540 (2008/02/05)
An efficient cross metathesis and Pd-catalyzed allylic rearrangement have been successfully used to construct the northern hemisphere of a cytotoxic marine natural product, palmerolide A. Georg Thieme Verlag Stuttgart.
Total synthesis of rhizoxin D, a potent antimitotic agent from the fungus Rhizopus chinensis
White, James D.,Blakemore, Paul R.,Green, Neal J.,Hauser, E. Bryan,Holoboski, Mark A.,Keown, Linda E.,Nylund Kolz, Christine S.,Phillips, Barton W.
, p. 7750 - 7760 (2007/10/03)
Rhizoxin D (2) was synthesized from four subunits, A, B, C, and D representing C3-C9, C10-C13, C14-C19, and C20-C27, respectively. Subunit A was prepared by cyclization of iodo acetal 21, which set the configuration at C5 of 2 through a stereoselective addition of the radical derived from dehalogenation of 21 at the β carbon of the (Z)-α,β-unsaturated ester. Aldehyde 29 was obtained from phenylthioacetal 24 and condensed with phosphorane 30, representing subunit B, in a Wittig reaction that gave the (E,E)-dienoate 31. This ester was converted to aldehyde 33 in preparation for coupling with subunit C. The latter in the form of methyl ketone 55 was obtained in six steps from propargyl alcohol. An aldol reaction of 33 with the enolate of 55 prepared with (+)-DIPCl gave the desired β-hydroxy ketone 56 bearing a (13S)-configuration in a 17-20:1 ratio with its (13R)-diastereomer. After reduction to anti diol 57 and selective protection as TIPS ether 58, the C15 hydroxyl was esterified to give phosphonate 59. An intramolecular Wadsworth-Emmons reaction of aldehyde 62, derived from δ-lactone 60, furnished macrolactone 63, which was coupled in a Stille reaction with stannane 68 to give 2 after cleavage of the TIPS ether.
Synthetic studies toward ansatrienines: Application of the Evans- Tishchenko reaction to chiral enones
Schoening, Kai-Uwe,Hayashi,Powell, Douglas R.,Kirschning, Andreas
, p. 817 - 820 (2007/10/03)
Practical syntheses of the C9-C14 sterotriade 5 and the C1-C8 polyene unit 6 in ansatrienine A (mycotriene) (1a), and other ansamycin antibiotics is described. A key step for controlling the configuration of the stereogenic center at C13 involves the stereoselective reduction of enone 10 using the Evans-Tishchenko reaction.
Super-acid Catalysed Addition of Allylsilanes to Carbonyl Compounds; Synthetic and Mechanistic Aspects
Davis, Anthony P.,Jaspars, Marcel
, p. 2111 - 2118 (2007/10/02)
The addition of allyltrimethylsilane 8 to a variety of aldehydes and one ketone (cyclohexanone) was found to be induced by the super-acid TfOH2(1+)B(OTf)4(1-) (Tf = CF3SO2).In contrast to the analogous Lewis acid catalysed reaction, only catalytic amounts
Acyclic Stereoselection. 22. Diastereofacial Selectivity in the Lewis Acid Mediated Reactions of Allylsilanes with Chiral Aldehydes and Enones
Heathcock, Clayton H.,Kiyooka, Syun-ichi,Blumenkopf, Todd A.
, p. 4214 - 4223 (2007/10/02)
The Lewis acid mediated reactions of chiral aldehydes 1-4 and enones 5-8 with allylsilanes 9 and 10 have been investigated.With aldehyde 1 and enones 5-7, modest diastereofacial preferences are seen, in the sense predicted by application of Felkin's model for asymmetric induction.Aldehydes 2-4 and enone 8 appear to react by way of chelated intermediates.With these four compounds, the diastereofacial preferences are rather large and are in the sense that is consistend with attack of the allylsilane on the least hindered face of the chelated intermediate.In the reaction of the trans and cis enones 6 and 8 with allyltrimethylsilane, a dramatic reversal of diastereofacial preference is observed; enone 6 gives a 84:14 ratio of products, while enone 8 provides a 10:90 mixture of the same products.
STEREOCHEMICAL CONSEQUENCES FOR THE LEWIS ACID MEDIATED ADDITIONS OF ALLYL AND CROTYLTRI-n-BUTYLSTANNANE TO CHIRAL β-HYDROXYALDEHYDE DERIVATIVES
Keck, Gary E.,Abbott, Duain E.
, p. 1883 - 1886 (2007/10/02)
Proper choice of Lewis acid and hydroxyl protecting group allows for selective addition of crotyltri-n-butylstannane to either face of the aldehyde carbonyl in derivatives of 2-methyl-3-hydroxypropanal with preservation of erythro selectivity for the bond
