106357-32-8Relevant academic research and scientific papers
The stereoselective synthesis of the C6-C18 fragment of scytophycin C employing a novel synthetic methodology
Yadav, Jhillu S.,Sunitha,Subba Reddy, Basi V.,Gyanchander
experimental part, p. 2933 - 2938 (2009/04/07)
A novel synthetic approach towards the stereoselective synthesis of the C6-C18 fragment of the biologically active antitumor agent scytophycin C is described. The synthesis involves Marouka allylation, base-catalyzed intramolecular conjugate addition, Wit
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.
Total synthesis of rutamycin B, a macrolide antibiotic from Streptomyces aureofaciens
White,Hanselmann,Jackson,Porter,Ohba,Tiller,Wang
, p. 5217 - 5231 (2007/10/03)
Rutamycin B (2) was synthesized from three principal subunits, spiroketal 75, keto aldehyde 83, and aldehyde 108. First, triol 62 was assembled by Julia coupling of sulfone 56 with aldehyde 58 followed by an acid-catalyzed spiroketalization. The three hydroxyl functions of 62 were successfully differentiated, leading to phosphonate 75. The latter was condensed in a Wadsworth-Emmons reaction with 83, prepared in six steps from (R)-aldehyde 76, to give 92. Coupling of the titanium enolate of 92 with 108 afforded Felkin product 109 with high stereoselectivity in a process that is critically dependent on the presence of the p-methoxybenzyl ether in the aldehyde. Transformation of 109 via aldehyde 116 to vinylboronate 122 was followed by macrocyclization under Suzuki conditions to yield 123. Exhaustive desilylation of the latter yielded rutamycin B.
Synthesis of the C1-C13 fragment of leucascandrolide A.
Crimmins,Carroll,King
, p. 597 - 599 (2007/10/03)
[reaction: see text] The synthesis of the C1-C13 fragment 3 of leucascandrolide A has been completed utilizing a stereoselective and regioselective reductive cleavage of a highly functionalized spiroketal to incorporate the cis-2,6-disubstituted tetrahydropyan. The spiroketal was constructed by addition of a lithiated pyrone 5 to aldehyde 6.
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.
Asymmetric Synthesis Using Tartrate Ester Modified Allylboronates. 2. Single and Double Asymmetric Reactions with Alkoxy-Substituted Aldehydes
Roush, William R.,Hoong, Lee K.,Palmer, Michelle A. J.,Straub, Julie A.,Palkowitz, Alan D.
, p. 4117 - 4126 (2007/10/02)
The reactions of tartrate allylboronates 1a and 1b with a series of chiral and achiral alkoxy-substituted aldehydes are described.It is shown that conformationally unrestricted α- and β-alkoxy aldehyde substituents have a significant, negative impact on the stereoselectivity of the asymmetric allylborations.For example, α-alkoxy aldehydes 25-27 and β-alkoxy aldehydes 28-30 undergo asymmetric allylborations with 1 in only 56-59percent and 63-66percent ee, respectively, while the reactions of 1 and aliphatic aldehydes such as decanal or cyclohexane-carboxaldehyde proceed in 86-87percent ee under the same conditions.Evidence of reduced stereoselection is also apparent in the double diastereoselectivity data reported in Table I and Scheme I for the asymmetric allylborations of chiral β-alkoxy aldehydes 16 and 19 and chiral α-alkoxy aldehyde 22.In contrast, chiral aldehydes containing alkoxy groups that are conformationally constrained by incorporation in rings, as in glyceraldehyde acetonide 4,4-deoxythreose ketal 7, and α,β-epoxy aldehydes 10 and 13, are excellent allylboration substrates, with diastereoselection in the cases of 4 and 7 being significantly greater than that obtained with simpler achiral substrates.A model that rationalizes this "alkoxy effect" is presented.Specifically, it is inferred that the observed trends in stereoselection are not steric in origin, but rather that unfavorable lon pair/lone pair interactions occur between the tartrate ester carbonyl and alkoxy substituents particularly of conformationally unconstrained aldehyde substrates (e.g., 16, 19, 22, 25-30) that results in diminished reaction stereoselection (see transition structures 58 and 61).For substrates with conformationally constrained alkoxy substituents , e.g. 4 and 7, favorable lone pair/dipole interactions between the tartrate ester carbonyl and the backside of the β-alkoxy C-O bond leads to increased stabilization of the favored transition state (see transition structures 59 and 60) and hence to increased reaction diastereoselection.A simple method for the analysis of the average diastereofacial selectivity of a chiral reagent in a pair of double asymmetric reactions is also presented.This analysis, which is independent of the intrinsic diastereofacial bias of the chiral aldehyde, enables one to make direct comparisons of the relative diastereoselectivities of a range of chiral substrates with a given chiral reagent (or vice versa).In this way, double diastereoselcetivity data are easily analyzed to determine if the chiral reagent/chiral substrate pair is "well behaved" compared to typical achiral substrate reference systems, thereby providing insight into the structural features that influence reaction stereoselectivity.
Chiral Synthesis via Organoboranes. 21. Allyl- and Crotylboration of α-Chiral Aldehydes with Diisopinocampheylboron as the Chiral Auxiliary
Brown, Herbert C.,Bhat, Krishna S.,Randad, Ramnarayan S.
, p. 1570 - 1576 (2007/10/02)
B-Allyldiisopinocampheylboranes have been screened for diastereofacial selectivity in their reaction with α-substituted chiral aldehydes.Both syn and anti products have been obtained in very high diastereoselectivities.Further, (E)-crotyldiisopinocampheylboranes and (Z)-crotyldiisopinocampheylboranes have been used for diastereofacial selectivity in their reaction with α-substituted chiral aldehydes.These crotylboranes, 20-23, are highly diastereoselective reagents and the corresponding (3,4- and 4,5-)-anti,syn, -anti,anti, and -syn,anti products have been obtained in very high facial selectivities; even the syn,syn product has been obtained in moderately good facial selectivity.Finally, the relative efficiences of the various chiral auxiliaries utilized in the literature for the allyl- and crotylboration have been compared with those achieved by the diisopinocampheylboron moiety.
N,N'-Dibenzyl-N,N'-ethylenetartramide: A Rationally Designed Chiral Auxiliary for the Allylboration Reaction
Roush, William R.,Banfi, Luca
, p. 3979 - 3982 (2007/10/02)
The chiral auxiliary designated in the title was designed as a probe of our previously suggested mechnism of asymmetric induction with tartrate allylboronates 1-3, namely that n/n electronic repulsive interactions between electron pairs on the aldehydic oxygen atom and an ester carbonyl disfavor transition-state C relative to A.The results reported for the new reagent 5 strongly support this thesis and suggest that the convergence of functional groups toward a metal center can be an exceedingly useful strategy for achieving a topological bias in the enantioselective functionalization of a carbonyl group.
