Zur Existenz niedergliedriger Cycloalkine, II

Wittig, Georg; Pohlke, R.

doi:10.1002/cber.19610941214

Cited by 88 publications

(21 citation statements)

References 15 publications

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“…More recent advances in this area include strain‐promoted azide–alkyne cycloadditions (SPAAC). These reactions, first observed more than 50 years ago,15 exploit the intrinsic ring strain of cyclooctynes 16. First generation substrates had relatively sluggish reactivity, and incremental improvements followed from the incorporation of a ring heteroatom, steric encumberments or electron‐attracting substituents; more recent rate enhancements have been observed with diaryl fused cyclooctynes and their aza analogues 17–25.…”

Section: Introductionmentioning

confidence: 99%

Circumferential resection margin as a prognostic factor in rectal cancer

Bernstein

Endreseth

Romundstad

et al. 2009

British Journal of Surgery

195

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Section: Introductionmentioning

confidence: 99%

Circumferential resection margin as a prognostic factor in rectal cancer

Bernstein

Endreseth

Romundstad

et al. 2009

British Journal of Surgery

195

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“…The products 23 and 24 could result from a spontaneous rearrangement of the initially formed Diels‐Alder adducts. It is known that the [4+2] cycloaddition adducts of DPBF and acetylenic dienophiles can undergo different rearrangements mainly under thermal, acidic (refluxing HOAc, HOAc/HCl at ambient temperature, chromatography on silica gel) and photochemical conditions . Thermal and acid‐catalyzed rearrangements can afford naphthalen‐1(2 H )‐ones and naphthalen‐2(1 H )‐ones, as in the case of DPBF/alkynylsulfone adducts .…”

Section: Resultsmentioning

confidence: 99%

Terminal Acetylenic Iminium Salts – Synthesis and Reactivity

et al. 2018

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Various types of terminal acetylenic iminium triflates (propyne iminium salts) featuring a ketiminium or an aldiminium group have been prepared for the first time by protiodesilylation of the corresponding trimethylsilyl‐substituted acetylenic iminium salts using triflic acid and catalytic silver(I) triflate. The high reactivity of the terminal C,C‐triple bond is documented herein by the facile Michael addition of nucleophiles and the exceptionally high dienophilic reactivity in Diels‐Alder reactions.

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“…The oxidation of the bis-hydrazone 57 to 56 can be rationalized by postulating a bis-carbene intermediate [50]. And the last two approaches [51] could also proceed via a vinylidene carbene, 59.…”

Section: Cyclohexyne and Its Derivativesmentioning

confidence: 99%

Angle‐Strained Cycloalkynes

Hopf¹,

Grunenberg²

2009

Strained Hydrocarbons

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IntroductionAccording to the sp-hybridization model, the carbon-carbon triple bond possesses a linear structure, and indeed, many alkynes fulfill this prediction. High level ab initio calculations [1] of isolated alkyne molecules, as well as gas phase electron diffraction experiments [2] reveal their linear minimum structure. On the other hand, given that the C C-R bending force constant becomes intrinsically smaller for substituted alkynes and polyynes, crystal packing effects may lead to deviations from strictly linear geometries [3]. From a dynamic point of view even in the case of acetylene one has to include the -albeit reduced -flexibility of the carboncarbon triple bond in order to describe, for example, the vinylidene acetylene rearrangement (see below) [4]. Further, the linear sp-hybrid picture only holds true for the electronic ground state. Cis-and trans-bent configurations are known in the case of low-lying electronic states [5]. Nevertheless, many alkynes correspond to the prediction of linearity due to the sp-hybrid model, and we have collected a selection of typical examples, reaching from the parent compound acetylene 1 via a few alkyl 2-4 and aryl acetylenes 5-7 to a functionalized acetylene, dimethyl acetylenedicarboxylate 8, in Scheme 7.1, together with the appropriate references [1, 2, 6-11], all dating from the recent literature.The easiest way to distort a triple bond is to incorporate it into a sufficiently small ring structure. The question, of course, is what this ring size is, and from what ring size on the respective cycloalkynes can we isolate compounds, that can be worked with under normal laboratory conditions [12]. Rather than using the nonspecific term 'distorted cycloalkyne' Krebs [12] prefers to speak of 'angle-strained cycloalkynes'. Since it is easier to deform a C C-C arrangement than its more hydrogenated olefinic and saturated analogs, relatively large angle deformations are possible in cycloalkynes without significant changes in energy. Krebs arbitrarily considers all cycloalkynes in which the C C-C angle is deformed by more than 10° as angle-strained [12]. Accepting this definition, the stable cyclononyne (see below) is an angle-strained cycloalkyne, whereas cyclodecyne is not.

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Zur Existenz niedergliedriger Cycloalkine, II

Cited by 88 publications

References 15 publications

Circumferential resection margin as a prognostic factor in rectal cancer

Circumferential resection margin as a prognostic factor in rectal cancer

Terminal Acetylenic Iminium Salts – Synthesis and Reactivity

Angle‐Strained Cycloalkynes

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