- Unprecedented migration of N-alkoxycarbonyl groups in protected pyroglutaminol.
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[figure: see text] Cleavage of an O-silyl ether in an N-BOC-protected pyroglutaminol using TBAF led to an unprecedented migration of the BOC group. An investigation of the mechanism, based on experimental data and quantum mechanical calculations, is presented. Similar migration was observed for N-Cbz and N-methoxycarbonyl groups.
- Bunch,Norrby,Frydenvang,Krogsgaard-Larsen,Madsen
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p. 433 - 435
(2007/10/03)
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- Lewis acid assisted vinylogous Mannich and Mukaiyama aldol reactions: A route to densely hydroxylated indolizidine alkaloid analogues
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The hydroxymethyl-substituted indolizidines 6 and 7, representative members of a ring-B-expanded alexine-australine subclass, are readily accessible by starting with furan-based silyloxydiene 12 and hydroxymethyl hemiaminal 11, through a synthesis sequence involving a scantily exploited vinylogous version of the Mannich reaction. The key iminium electrophilic acceptor 11 is, in turn, available through a vinylogous intermolecular Mukaiyama aldolization process between pyrrole-based silyloxydiene 8 and (S)- glyceraldehyde 9.
- Rassu, Gloria,Carta, Paola,Pinna, Luigi,Battistini, Lucia,Zanardi, Franca,Acquotti, Domenico,Casiraghi, Giovanni
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p. 1395 - 1400
(2007/10/03)
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- Expeditious syntheses of sugar-modified nucleosides and collections thereof exploiting furan-, pyrrole-, and thiophene-based siloxy dienes
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A series of individual sugar-modified pyrimidine nucleosides including enantiomerically enriched 2',3'-dideoxynucleosides 14a-c (α and β anomers of L- and D-series), 2',3'-dideoxy-4'-thionucleosides 21a-c (α and β anomers of L- and D-series), and 2',3'-dideoxy-4'-azanucleosides 28a-c (β anomers of L- and D-series) were synthesized, with uniform chemistry and high stereochemical efficiency, exploiting a triad of versatile heterocyclic siloxy dienes, namely, 2-(tert-butyldimethylsiloxy)furan (TBSOF), 2-(tert- butyldimethylsiloxy)thiophene (TBSOT), and N-(tert-butoxycarbonyl)-2-(tert- butyldimethylsiloxy)pyrrole (TBSOP). The synthetic procedure advantageously used both enantiomers of glyceraldehyde acetonide (D-1 and L-1) as sources of chirality and as synthetic equivalents of the formyl cation. The outlined chemistry also allowed for the rapid assemblage of a 30-member collection of racemic nucleosides (D,L-L) as well as one 15-member ensemble of chiral analogues (L-L), along with some related sublibraries.
- Rassu, Gloria,Zanardi, Franca,Battistini, Lucia,Gaetani, Enrico,Casiraghi, Giovanni
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p. 168 - 180
(2007/10/03)
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- Total syntheses of N-boc-protected 3′-deoxy-4′-azathymidine and 4′-azauridine
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Novel modified nucleosides 4, 11, ent-11, and 17, wherein the furanose ring oxygen is replaced by nitrogen, have been synthesized by reacting azasugars 3, 10, ent-10, and 15 with silylated uracil or thymine bases.
- Rassu, Gloria,Pinna, Luigi,Spanu, Pietro,Ulgheri, Fausta,Casiraghi, Giovanni
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p. 4019 - 4022
(2007/10/02)
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- Synthesis of (3R,4R,5R)-1-(tert-butoxycarbonyl)-3,4-isopropylidenedioxy-5-methoxyme thyl-2-pyrrolidinone from (S)-pyroglutaminol
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(3R,4R,5R)-1-(tert-Butoxycarbonyl)-3,4-isopropylidenedioxy-5-methoxyme thyl-2-pyrrolidinone (6), a useful chiral intermediate for the preparation of calyculins, was synthesized starting from (S)-pyroglutaminol via the O-methylation of 1c with diazomethane in the presence of fluoboric acid and cis-dihydroxylation of the α,β-unsaturated lactam (4) as the key reactions.
- Ikota
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p. 1925 - 1927
(2007/10/02)
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