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Dithiane-epoxide coupling

Smith et al. have developed a very elegant route to complex polyol structures by sequential dithiane-epoxide coupling reactions (Scheme 7) [16]. Following the work of Tietze [17], 2-silyl-1,3-dithianes 42 are deprotonated with /BuLi in ether and converted into the stable lithium alk-oxides 43 with enantiomerically pure epoxides. A fast 1,4-Brook rearrangement occurs only after the addition of 0.3 equivalents of hexamethyl-phosphoramide (HMPA) or 1,3-dimethylhexahy-dro-2-pyrimidone (DMPU) to the reaction mixture. A new lithiated dithiane 44 that can undergo... [Pg.62]

Scheme 8.31 Smith Ill s three- and multicomponent linchpin coupling of metalated silyl dithiane 109 with epoxides. Scheme 8.31 Smith Ill s three- and multicomponent linchpin coupling of metalated silyl dithiane 109 with epoxides.
The multicomponent linchpin coupling of silyl dithianes with epoxides was very efficiently used to access both the AB and CD spiroketal fragments of spongistatin. [Pg.293]

Assembling a five-component coupling product in a single operation further extended this methodology. Following alkylation of dithiane 78 with epoxide (—)79 (2.6 equivalent each) to generate the unrearranged alkoxy dithiane 80, sequential addition of HMPA and (—)-epichlorohydrin 81 (1 equivalent) furnished the bis(silyloxy dithiane) carbinols (- -)82 in 66% yield (equation 29) . ... [Pg.472]

Sunay, U. Fraser-Reid, B. Synthetic studies relating to the C1-C9 eastern" half of rosara-micin. Tetrahedron Lett. 1986, 27, 5335-5338. Smith, A. B. Pitram, S. M. Boldi, A. M. Gaunt, M. J. Sfouggatakis, C. Moser, W. H. Multicomponent linchpin couplings. Reaction of dithiane anions with terminal epoxides, epichlorohydrin, and vinyl epoxides efficient, rapid, and stereocontrolled assembly of advanced fragments for complex molecule synthesis./. Am. Chem. Soc. 2003, 125, 14435— 14445. [Pg.137]

Let us turn now to the other coupling partner, aldehyde 58 it was synthesised by the pathway shown in Scheme 17.18. The first step was a Sharpless catalytic asymmetric epoxidation on ( )-crotyl alcohol with the oxidant derived from (—)-diethyl tartrate. An in situ derivatisation with r-butyldiphenylsilylchloride was then performed. The desired epoxide 59 was readily isolated in 76% overall yield after chromatography. Treatment of 59 with 2-lithio-l,3-dithiane in THF and 1,3-dimethyl-3,4,5,6-tetrahydro-2(l/7)-pyrimidinone (DMPU also known as N,N-... [Pg.314]

Multicomponent linchpin couplings can be carried out with 2-trialkylsilyl substituted 1,3-dithianes 207 and epoxides and was successfully used in the synthesis of natural products182. Tietze and coworkers303 found out that 2-lithio-2-trimethylsilyl-1,3-dithiane 208 reacted with two equivalents of a chiral epoxides in the presence of a crown ether to give first the monoadduct 209, which suffered 1,4-Brook rearrangement304 generating a new dithiane anion 210. Final reaction with an epoxide afforded products 211, which are equivalents of acetone aldol products (Scheme 60). [Pg.174]

The location of the silyl protecting group in the coupling product from the reaction between a silyl dithiane and two different chiral epoxides is controlled by the order of the addition of the epoxides. Subsequent cyclisation of the derived 1,3-diketones provides an efficient route to a variety of 2,6-disubstituted dihydropyran-4-ones 39 <07JOC4280>. [Pg.414]

The stereocontrolled enantioselective synthesis of an advanced B-ring synthon of bryostatin 1 was achieved in the laboratory of K.J. Hale. " The key step was a Smith-Tietze coupling of 2-lithio-2-TBS-1,3-dithiane with a homochiral epoxide in the presence of HMPA. The resulting dithiane alkoxide was trapped with TBSCI in situ followed by deprotection of the dithiane moiety to give a Crsymmetrical ketone. This ketone was then further elaborated into the target B-ring synthon. [Pg.419]

Coupling of the two fragments 92 and 98 took place via lithiation of the vinyl stannane and conversion to the cuprate, followed by addition to epoxide 92 to give 99 in 89% yield. Conversion of 99 (R = MTM) to bis-silyl ether 100 was accomplished in 85% yield utilizing conventional methods. Homologation by a two-carbon unit was achieved by metalation of the dithiane group followed by the addition of dimethyloxalate to give the a-keto ester 101 in 96% yield. [Pg.116]

The syntheses of the C1-C12 AB and C13-C28 CD segments, 528 and 535, are summarized in Scheme 75. The syntheses of the two segments are based on a one-pot unsymmetric bisalkylation of 2-TBS-l,3-dithiane (525) with Brook rearrangement. Epoxides 521, 522, 523, and 524 were synthesized as coupling partners. [Pg.252]

An approach to the 1,3-polyol system complementary to that shown in Schemes 83 and 84 makes use of dithiane 598 as a synthetic equivalent of 603. Alkylation of the anion generated from 598 with epoxide 303 gives the coupled dithiane 599. After hydrolysis of the thioacetal, a 57 -selective reduction of ketone 600 with lithium aluminum hydride in the presence... [Pg.242]

In addition, the linear approach was represented by sequential dithiane coupling [21] of the epoxides for the necessary fragments to either side of the ketone function at C21. Another approach uses microbial reduction (baker s yeast) to set the stereocenter at C25 before elaboration of that fragment into a methyl acetylenic ketone [89]. This acetylenic ketone was condensed with the aldehyde partner representing Cl5-19 to give the aldol adduct which was cyclized in acid to afford a precursor similar to those obtained from acetylide addition to lactone B 3. Yet another linear assembly pathway involves the alkylation of the portion containing C23-27 of 22,23-dihydroavermectin B to the dianion of 2,4-pentanedione followed by another condensation to 3-be-nzyloxypropanal [108]. Subsequent acidic cyclization and standard chemistry provided the thermodynamic spiroketal. [Pg.81]

The key reaction of the second synthesis of (+)-104 by Inoue-Hirama s group [75-79] was intramolecular alkylation of nitrile-epoxide 168 to form the G-ring, and dithiane coupling and olefin metathesis [80-82] with BCD-ring fragment 169 for macrocyclization (Scheme 17). [Pg.101]

One of the most used sequential component reactions in the asymmetric construction of chiral compounds is the so-called anion relay chemistry (ARC) [2], This linchpin coupling protocol consists in the alkylation of an anion, generally a silyl lithium dithiane derivative, by an epoxide or an aziridine, resulting in an oxy- or aza-anion, which in the presence of hexamethylphosphoramide (HMPA) or other polar solvent gives a 1,4-Brook rearrangement, thereby leading to a new reactive dithiane anion that is capable of reacting with a second electrophile E+ (Scheme 11.1). [Pg.310]

To further broaden the substrate scope and stereochemical outcome of the organocatalytic oxa-conjugate reaction, different a,j -unsaturated aldehydes (Z)-2.39a-e with a variety of substituents at the C(6) position were prepared by dithiane coupling reaction of (Z)-2.36 a-e with commercially or readily available chiral epoxides 2.37a-e (Scheme 2.5). [Pg.39]


See other pages where Dithiane-epoxide coupling is mentioned: [Pg.14]    [Pg.14]    [Pg.21]    [Pg.63]    [Pg.419]    [Pg.229]    [Pg.161]    [Pg.702]    [Pg.291]    [Pg.293]    [Pg.176]    [Pg.1701]    [Pg.418]    [Pg.249]    [Pg.255]    [Pg.108]    [Pg.175]    [Pg.129]    [Pg.130]    [Pg.186]    [Pg.3]    [Pg.287]    [Pg.607]    [Pg.259]    [Pg.265]    [Pg.92]    [Pg.1118]    [Pg.617]   
See also in sourсe #XX -- [ Pg.14 , Pg.30 ]

See also in sourсe #XX -- [ Pg.14 ]




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