Stereochemistry of the [2+2] Cycloaddition of Chlorosulfonyl Isocyanate to Chiral Alkoxyallenes Derived from 1,3‐Alkylidene‐<scp>L</scp>‐erythritol and ‐<scp>D</scp>‐threitol

Danh, Tong Thanh; Bocian, Wojciech; Kozerski, Lech; Szczukiewicz, Patrycja; Frelek, Jadwiga; Chmielewski, Marek

doi:10.1002/ejoc.200400557

Cited by 13 publications

(4 citation statements)

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“…The rule was demonstrated experimentally to be correct for a variety of oxacephams. 8,9 It was also found that the same rule is valid for clavams. 10,11 This helicity rule for both oxacephams and clavams was established empirically on the basis of X-ray structures and the tentative assignment of the electronic transition at $220 (oxacephams) and 240 nm (clavams) to an np* amide transition in the azetidinone system.…”

Section: Introductionmentioning

confidence: 64%

“…Most probably, however, the CD band represents a sum of contributions from the amide and benzene ( 1 L b ) chromophores present in these molecules. In the respective UV spectra, the electronic absorption of y The crystallographic data for structures 9 phenyl group is clearly visible at ca. 257 nm and possesses characteristic fine structure (Table 1).…”

Section: Results and Disscusion Experimental Uv And Ecd Spectra Of CLmentioning

confidence: 97%

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Structure–chiroptical properties relationship in clavams: An experimental and theoretical study

et al. 2007

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It is well known that the biological activity of clavams depends strongly on the absolute configuration at the ring junction carbon atom. Therefore, development of the efficient stereo-controlled synthetic methods for the new oxygen analogs of penams, and the structure-activity relationship studies call for a reliable determination of the absolute stereochemistry of newly synthesized compounds. Recently, we proposed an empirical helicity rule relating the configuration of the bridgehead carbon atom to the sign of the 240 nm band observed in the electronic circular dichroism (ECD) spectrum of clavams. In the present work, we investigate the validity of this structure-property relationship for several enantiomeric pairs of model compounds possessing an additional, interfering chromophore in the molecule. For this purpose a combination of the ECD spectroscopy and the time-dependent density functional theory (TD-DFT) is used. A comparison of the ECD spectra with the theoretical ones obtained by the TD-DFT calculations gives a reasonable interpretation of the Cotton effects observed in the 250-220 nm spectral range. Moreover, the calculations confirm validity of the helicity rule for systems studied here and demonstrate that ECD spectroscopy may be used as a highly sensitive probe of the three-dimensional molecular structure of clavams.

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Section: Introductionmentioning

confidence: 64%

Section: Results and Disscusion Experimental Uv And Ecd Spectra Of CLmentioning

confidence: 97%

Structure–chiroptical properties relationship in clavams: An experimental and theoretical study

et al. 2007

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“…The [2 þ 2] cycloaddition of chlorosulfonyl isocyanate (CSI) to alkoxyallenes derived from ethylidene and benzylidene erythritols and threitols proceeds with a moderate asymmetric induction in the case of the erythritols (Scheme 24.6) and with a very low induction in the case of threitols. This indicates that the erythritol derivatives may exist in solution in one predominant conformation while the threitol derivatives behave as a conformational ensemble [50].…”

Section: Isocyanate-alkene Cyclocondensationmentioning

confidence: 99%

The Chemistry of 2‐Azetidinones (β‐Lactams)

Alcaide¹,

Almendros²,

Luna³

2011

Modern Heterocyclic Chemistry

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The large number of recent reports on b-lactam chemistry demonstrates the increasing interest in this important class of compounds. Monocyclic b-lactams frequently serve as precursors for the synthesis of classical bicyclic b-lactam antibiotics. The cyclic 2-azetidinone skeleton has been extensively used as a template on which to build the heterocyclic structure fused to the four-membered ring, using the chirality and functionalization of the b-lactam nucleus as a stereocontrolling element. The discovery of nonclassical b-lactam antibiotics, such as monobactams and nocardicins, coupled with ever-growing new applications such as enzyme inhibition has triggered a renewed interest in the building of new monocyclic b-lactam derivatives. Besides the utility of b-lactams as biologically active agents, they are used as intermediates in a-and b-amino acid synthesis, as well as building blocks for alkaloids, heterocycles, taxoids and other types of compounds of biological and medicinal interest. Physicochemical Data Computational ChemistryTheoretical studies show that b-lactams are weaker bases, in the gas phase, than acyclic amides [1]. The attenuation of basicity upon cyclization is stronger than that found for cyclic ketones of similar size due to the existence of a negative hyperconjugation effect that is present in b-lactams but not in cyclic ketones. Ab initio calculations indicate that both b-lactams and acyclic amides are oxygen bases, but the gap between the oxygen and nitrogen intrinsic basicities is much smaller in the former due to the aforementioned cyclization effects. This decrease of the oxygen Modern Heterocyclic Chemistry, First Edition. Edited

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“…碱催化体系(NaOH 或 EtONa/EtOH)下, 4-乙酰氧基氮杂环丁酮同样可发生亲核取代离去乙酰基团, 缩合反应闭环形成苯并氧头孢 [79,80] (Scheme 13). [107,108] , alkylidenecephalosporins [109] 等抗生素, 环外双键对其生物活性均产生重要影响 [110] . (2) [138,139] .…”

Section: -乙烯氧基氮杂环丁酮的乙烯氧基在一定条件下unclassified