Divergent Reactivity of 2‐Azetidinone‐Tethered Allenols with Electrophilic Reagents: Controlled Ring Expansion <i>versus</i> Spirocyclization

Alcaide, Benito; Almendros, Pedro; Luna, Amparo; Torres, M. Rosario

doi:10.1002/adsc.200900864

Cited by 45 publications

(14 citation statements)

References 66 publications

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“…Related semipinacol-like ring expansions of non-fused β-lactams to γ-lactams have been reported in the literature, and notably all occur with exclusive migration of the N -acyl group rather than the methylene or methine carbon atom (Scheme 3 ). [ 21 ]–[ 23 ] Our approach was also inspired by the X-ray crystal structure of β-lactam 2 , in which the cyclohexane ring adopts a boat-like arrangement to accommodate the cis -ring fusion, placing the diethyldithiocarbamate group axial with the C–S bond approximately antiperiplanar with the C–C(O) bond of the β-lactam (C1-C2-C7-S1 torsion angle −173.2 (2)°) (Figure 2 ). [ 24 ] In as much as 2 can be regarded as a model for the proposed rearrangement precursor 10 , migration of the N -acyl group of the β-lactam was expected to be preferred both electronically and stereoelectronically over migration of the N -alkyl group.…”

Section: Introductionmentioning

confidence: 99%

Carbamoyl Radical‐Mediated Synthesis and Semipinacol Rearrangement of β‐Lactam Diols

Betou

Male

Steed

et al. 2014

Chemistry A European J

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In an approach to the biologically important 6-azabicyclo[3.2.1]octane ring system, the scope of the tandem 4-exo-trig carbamoyl radical cyclization—dithiocarbamate group transfer reaction to ring-fused β-lactams is evaluated. β-Lactams fused to five-, six-, and seven-membered rings are prepared in good to excellent yield, and with moderate to complete control at the newly formed dithiocarbamate stereocentre. No cyclization is observed with an additional methyl substituent on the terminus of the double bond. Elimination of the dithiocarbamate group gives α,β- or β,γ-unsaturated lactams depending on both the methodology employed (base-mediated or thermal) and the nature of the carbocycle fused to the β-lactam. Fused β-lactam diols, obtained from catalytic OsO4-mediated dihydroxylation of α,β-unsaturated β-lactams, undergo semipinacol rearrangement via the corresponding cyclic sulfite or phosphorane to give keto-bridged bicyclic amides by exclusive N-acyl group migration. A monocyclic β-lactam diol undergoes Appel reaction at a primary alcohol in preference to semipinacol rearrangement. Preliminary investigations into the chemo- and stereoselective manipulation of the two carbonyl groups present in a representative 7,8-dioxo-6-azabicyclo[3.2.1]octane rearrangement product are also reported.

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Section: Introductionmentioning

confidence: 99%

Carbamoyl Radical‐Mediated Synthesis and Semipinacol Rearrangement of β‐Lactam Diols

Betou

Male

Steed

et al. 2014

Chemistry A European J

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“…2-Azetidinone-tethered allenols 37 have been used to obtain tetramic acids 38 using brominating reagents (Scheme 12) [23]. After testing with different halogen sources such as molecular iodine, NBS, NIS, TBCA, and Ipy 2 BF 4 , two optimal conditions were found: (a) the use of NBS in dichloromethane at room temperature and (b) the use of TBCA in a mixture of tetrahydrofuran and water at room temperature.…”

Section: Synthesis Of Five-membered Heterocyclesmentioning

confidence: 99%

Ring Expansions of β-Lactams and β-(thio)lactones

Alcaide

Almendros

Aragoncillo

2015

Topics in Heterocyclic Chemistry

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The skeleton of β-lactams and β-lactones is present in biologically active compounds. For example, the β-lactam ring is present in classical antibiotics such as penicillins and cephalosporins. On the other hand, there are several natural products containing a β-lactone moiety, with interesting inhibitory activity. In addition, both fragments are very useful synthetic intermediates for the preparation of cyclic and acyclic compounds. The ring strain present in both motifs is involved in this versatile reactivity. This chapter is devoted to the synthesis of five-to sevenmembered heterocycles by ring expansion of β-lactams and β-lactones. Different methodologies have been described, and the mechanism for the formation of the products has been discussed. In addition, the applicability of some of the processes has been demonstrated by the synthesis of fragments of natural or biologically relevant compounds. The contributions presented in this chapter have been selected mainly from the developments achieved in the last decade.

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“…machten die interessante Beobachtung, dass elektronenreiche Arene in Kombination mit I + als Nukleophil in intermolekularen elektrophilen Additionen an einfache Allene auftreten können 254. Darüber hinaus lieferten die Reaktionen von sekundären oder tertiären 2,3‐Allenolen mit X + über die 1,2‐Verschiebung einer Aryl‐ oder Alkylgruppe 2‐Halogen‐2‐propenylketone oder 3‐Halogen‐3‐enale, die auf anderem Weg nicht leicht erhältlich sind (Schema ) 173k. 255…”

Section: Ausblickunclassified

Poly(1,4‐cyclohexylenedimethylene‐1, 4‐cyclohexanedicarboxylate): analysis of parameters affecting polymerization and cis–trans isomerization

Colonna¹,

Berti²,

Binassi³

et al. 2011

Polymer International

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Weatherable semicrystalline polyesters based on 1,4-cyclohexanedimethanol, 1,4-cyclohexanedicarboxylic acid (CHDA) or dimethyl 1,4-cyclohexane dicarboxylate (DMCD) can be prepared under normal melt-phase conditions, using titanium tetrabutoxide as catalyst. The effect of monomer ratio, reaction temperature and catalyst loading on the final polymer properties was studied. Under the proper polymerization conditions, poly(1,4-cyclohexylenedimethylene-1,4-cyclohexanedicarboxylate) polymers with high molecular weight can be obtained. During polymerization, isomerization can occur towards the thermodynamically stable cis-trans ratio of 34-66 mol%. Carboxylic acid end groups can catalyze the isomerization and therefore the polymerization is more critical starting from CHDA rather than DMCD. Moreover, temperature control becomes a key factor to avoid or to limit isomerization. The study of the isomerization of the different monomers permitted a better understanding of the isomerization and therefore of the polymerization process

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Divergent Reactivity of 2‐Azetidinone‐Tethered Allenols with Electrophilic Reagents: Controlled Ring Expansion versus Spirocyclization

Cited by 45 publications

References 66 publications

Carbamoyl Radical‐Mediated Synthesis and Semipinacol Rearrangement of β‐Lactam Diols

Carbamoyl Radical‐Mediated Synthesis and Semipinacol Rearrangement of β‐Lactam Diols

Ring Expansions of β-Lactams and β-(thio)lactones

Poly(1,4‐cyclohexylenedimethylene‐1, 4‐cyclohexanedicarboxylate): analysis of parameters affecting polymerization and cis–trans isomerization

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