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Roush reaction

Treatment of 122 with (R,R)-tartrate crotyl-boronate (E.R.R)-W 1 provides the alcohol corresponding to 123 with 96% stereoselectivity. Benzylation of this alcohol yields 123 with 64% overall yield. The crude aldehyde intermediate obtained by ozonolysis of 123 is again treated with (Z,R,R)-111 (the second Roush reaction), and a 94 5 1 mixture of three diastereoisomers is produced, from which 124 can be isolated with 73% yield. A routine procedure completes the synthesis of compound 120, as shown in Scheme 3-44. Heating a toluene solution of 120 in a sealed tube at 145°C under argon for 7 hours provides the cyclization product 127. Subsequent debromination, deacylation, and Barton deoxygenation accomplishes the stereoselective synthesis of 121 (Scheme 3-44). [Pg.172]

Intermolecular cycloadditions or Diels-Alder reactions have proved to be a successful route to several valuable intermediates for natural product syntheses. In creating new chiral centers, most of these reactions apply single asymmetric induction. As mentioned in Chapter 3, in the asymmetric synthesis of the octa-hydronaphthalene fragment, the Roush reaction is used twice. Subsequent intramolecular cyclization leads to the key intermediate, the aglycones, of several natural antitumor antibiotics. On the other hand, the Diels-Alder reaction of a dienophile-bearing chiral auxiliary can also be used intramolecularly to build... [Pg.301]

In conclusion, the Sakurai reaction is a powerful method to introduce a nucleophilic allyl synthon. Similar allylations include the Keck reaction of allylstannanes, and the Roush reaction of allylboranes. What sets the Sakurai reaction apart is the exceptional stability of allylsilanes, which are stable to air and water, and can easily be chromatographed, unlike most other allylmetal species. In addition, allylsilanes are easily accessible by a variety of reactions. These factors have allowed the Sakurai reaction to find widespread use, from basic methodology to total synthesis. [Pg.568]

W. R. Roush in Allylorganometallics The Uncatalyzed Reaction of Allylorganometallics with C = X Electrophiles in Comprehensive Organic Synthesis, C. H. Heathcock, Ed., Vol. 2, Perga-mon. Oxford 1991. [Pg.217]

The minimization of gauche pentane interactions in the transition stales is also an important consideration in the reactions of substituted allylboronates and a-heteroatom-substituted aldehydes4,52d 54,56. Transition states 8 and 11 have been identified by Roush and Hoffmann as the least sterically hindered ones accessible in reactions with (E)- and (Z)-allylboronates. [Pg.285]

Chlorothricolide, the aglycon of the chlorothricin antibiotic, is a complex molecule containing an octahydronaphthalene unit. Roush and Sciotti [121] recently reported the total enantioselective synthesis of chlorothricolide. The multiple Diels-Alder reaction between poliene 130 and chiral dienophile (R)-131 was the key step in the synthetic process (Scheme 2.50). The interaction... [Pg.78]

Roush W. R. Stereochemical and Synthetic Studies of the Intramolecular Diels-Alder Reaction Adv. Cycloaddit. 1990 2 91-146... [Pg.324]

For clarification, individual transformations of independent functionalities in one molecule - also forming several bonds under the same reaction conditions -are not classified as domino reactions. The enantioselective total synthesis of (-)-chlorothricolide 0-4, as performed by Roush and coworkers [8], is a good example of tandem and domino processes (Scheme 0.1). I n the reaction of the acyclic substrate 0-1 in the presence of the chiral dienophile 0-2, intra- and intermolecular Diels-Alder reactions take place to give 0-3 as the main product. Unfortunately, the two reaction sites are independent from each other and the transformation cannot therefore be classified as a domino process. Nonetheless, it is a beautiful tandem reaction that allows the establishment of seven asymmetric centers in a single operation. [Pg.2]

William R. Roush is Warner Lambert/Parke Davis Professor of Chemistry at the University of Michigan. He received his B.S. from the University of California, Los Angeles, in 1974 and his Ph.D. from Harvard University in 1977. His research area is organic chemistry, with specialized interests in organic synthesis and natural products chemistry, stereochemistry of organic reactions, development of new methods and regents, asymmetric synthesis, and oligosaccharide synthesis. [Pg.200]

The use of tartrates as chiral auxiliaries in asymmetric reactions of allenyl bor-onic acid was first reported by Haruta et al.69 in 1982. However, it was not for several years that Roush et al.,70 after extensive study, achieved excellent results in the asymmetric aldol reactions induced by a new class of tartrate ester based allyl boronates. [Pg.168]

Addition to chiral aldehydes. Brown et al.2 have examined the reaction of the chiral aldehyde 2 with the (E)- and (Z)-isomers of (+)- and (- )-l. The stereochemistry at the newly formed bond between C4 and C5 is controlled by the chirality of 1. The reaction affords two of the possible diastereomeric products in 64% de. Similar results have been reported by Roush et al. for reaction of a (3-alkoxy-a-methyl aldehyde. [Pg.103]

The glycosylation based on the Mitsunobu reaction has been most commonly directed to the synthesis of O-aryl glycosides, a structural motif found in a variety of natural products [80-82], Early work by Grynkiewicz [83,84], among others [85-87], established the viability of triphenylphosphine and diethylazodicarboxylate to promote the glycosylation of phenol acceptors at ambient temperature. More recently, Roush and coworkers have discovered that the glycosylation performed well in the... [Pg.123]

The sulfone moiety was reductively removed and the TBS ether was cleaved chemoselectively in the presence of a TPS ether to afford a primary alcohol (Scheme 13). The alcohol was transformed into the corresponding bromide that served as alkylating agent for the deprotonated ethyl 2-(di-ethylphosphono)propionate. Bromination and phosphonate alkylation were performed in a one-pot procedure [33]. The TPS protecting group was removed and the alcohol was then oxidized to afford the aldehyde 68 [42]. An intramolecular HWE reaction under Masamune-Roush conditions provided a macrocycle as a mixture of double bond isomers [43]. The ElZ isomers were separated after the reduction of the a, -unsaturated ester to the allylic alcohol 84. Deprotection of the tertiary alcohol and protection of the prima-... [Pg.91]

The presence of a stereogenic center on the aldehyde can strongly inlinence the diastereoselectivity in allylboration reactions, especially if this center is in the a-position. Predictive rules for nucleophilic addition on snch a-snbstitnted carbonyl substrates such as the Felkin model are not always snitable for closed transition structures.For a-substituted aldehydes devoid of a polar substituent, Roush has established that the minimization of ganche-ganche ( syn-pentane ) interactions can overrule the influence of stereoelectronic effects. This model is valid for any 3-monosubstituted allylic boron reagent. For example, althongh crotylboronate (E)-7 adds to aldehyde 39 to afford as the major prodnct the diastereomer predicted by the Felkin model (Scheme 2), " it is proposed that the dominant factor is rather the minimization of syn-pentane interactions between the Y-snbstitnents of the allyl unit and the a-carbon of the aldehyde. With this... [Pg.25]

See also the Masamune-Roush conditions for this reaction. Generally useful for base-sensitive aldehydes. [Pg.334]

D. F. Taber, Intramolecular Diels-Alder and Ene Reactions, Springer-Verlag, New York, 1984 see also W. R. Roush, in Comprehensive Organic Synthesis , ed. L. A. Paquette, Pergamon Press, New York, 1991, vol. [Pg.1166]

The same reaction was studied by Roush et al. [50]. However, in this case, the cyclization of anti-allylsilane 126 resulted in the production of only cis-2,6-disubstituted dihydropyrans 127. No trans-2,6-disubstituted dihydropyrans 128 were formed. Moreover, significant amounts of adducts 129 and 130 were observed (Scheme 13.45). These products probably originate from a side-chain exchange process (vide infra). [Pg.420]

W. R. Roush, D. P. Sebesta, and R. A. James, Stereoselective synthesis of 2-deoxy-p-glycosides from glycal precursors. 2. Stereochemistry of glycosidation reactions of 2-thiophenyl- and 2-selenophenyl-a-D-g/uco-pyranosyl donors, Tetrahedron, 53 (1997) 8837-8852. [Pg.204]

S CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Dennis P. Curran. Intramolecular 1,3-Dipolar Cycloaddition Chemistry, Albert Padwa and Allen M. Schoffstall. Stereochemical and Synthetic Studies of the Intramolecular Diels-Alder Reaction, William R. Roush. Thermal Reaction of Cyclopropenone Ketals, Key Mechanistic Features, Scope and Application of the Cycloaddition Reactions of Cyclopropenone Ketals and p - Delocalized Singlet Vinyl Carbenes Three Carbon 1,1-/1,3-Dipoles, Dale L. Boger and Christine E. Brotherton-Pleiss. Index. [Pg.226]


See other pages where Roush reaction is mentioned: [Pg.168]    [Pg.172]    [Pg.514]    [Pg.145]    [Pg.168]    [Pg.172]    [Pg.514]    [Pg.145]    [Pg.165]    [Pg.283]    [Pg.619]    [Pg.311]    [Pg.1151]    [Pg.186]    [Pg.169]    [Pg.170]    [Pg.198]    [Pg.139]    [Pg.369]    [Pg.22]    [Pg.7]    [Pg.839]    [Pg.73]    [Pg.29]    [Pg.20]    [Pg.34]    [Pg.631]    [Pg.17]   


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