Synthese und Solvolyse von (<i>Z</i>)/(<i>E</i>)‐1‐Methyl‐2‐[2‐(1‐propin‐1‐yl)phenyl]vinyl‐triflat und 1‐Methylen‐2‐[2‐(1‐propin‐1‐yl)‐phenyl]ethyl‐triflat

The synthesis of 3,4-ene-1,5-diynes, the key structural moiety present in several naturally occurring antitumor antibiotics, from 1,2-enedialdehydes under two different experimental conditions is reported. One method involves the dibromomethylenation of dialdehydes under Corey-Fuchs conditions (CBr 4 , Ph 3 P, and Zn) and treatment of the resulting tetrabromides with nBuLi or LDA to afford enediynes. The second method involves a base-mediated reaction of enedialdehydes with diethyl (1-diazo-2-oxopropyl)phosphonate (Bestmann-Ohira reagent) and subsequent transformation of the bis(diazo) compounds generated in situ to enediynes. While the transformation of bis(diazo) compounds to enediynes could take place exclusively through alkylidenecarbenes, generated in situ by geminal elimination of N 2 , an

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“…MS (EI): m / z (%) = 154 (100) [M] + , 152 (70), 128 (10), 115 (8), 76 (20). These data are in agreement with literature data 68b…”

Section: Methodssupporting

confidence: 93%

Synthetic and Mechanistic Investigations on the Rearrangement of 2,3‐Unsaturated 1,4‐Bis(alkylidene)carbenes to Enediynes

2007

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“…In some instances, the π system of the alkyne can act as a nucleophile if the terminal alkene is sufficiently activated. The most fundamental example of this type of reactivity is demonstrated by the work of Hanack and co-workers who have studied the cycloaromatization of vinyl triflate dienyne 49 (Scheme ) . Upon heating in a basic buffered media, 49 was proposed to ionize to alkyne-stabilized vinyl cation 50 .…”

Section: Nucleophilic Attack By the Alkynementioning

confidence: 99%

Acceleration of Conjugated Dienyne Cycloaromatization

Hitt

O’Connor

2011

Chem. Rev.

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The most surprising observation was the high degree of rate acceleration in the presence of amine bases, which was determined to be an order of magnitude higher than molecular oxygen acceleration and 4 orders of magnitude higher than hydrogen abstraction from solvent. Use of C-2 deuterium enriched 9 with amine showed high levels of D incorporation in the C-2 position of 11 under all conditions. Furthermore, in the absence of amine under identical open-air conditions, negligible deuterium incorporation in 11 was observed, ruling out an intramolecular [1,5]-H transfer. On the basis of these results, a deprotonation/ reprotonation mechanism was proposed to proceed through aryl anion 15. Laarhoven and co-workers have also obtained similar findings for the photocycloaromatizations of Type II-internal dienynes. 9 Key insight into the reactive excited state of the photocycloaromatization came through the work of Lewis and Sajimon who studied the reactivity of various Type II-internal dienynes with varying substitution at the terminal alkene. 10 These researchers hypothesized that the efficiency of the cyclization would increase if a higher proportion of the terminal alkene existed in the less stable syn conformation, 16-syn, versus the anti conformation, 16-anti (Table 1). To test this prediction, dienynes 16-Me and 16-cy were prepared with the expectation that 16-Me would increase the concentration of rotomer 16-syn and 16-cy would lock the dienyne in the syn conformation. As expected, the quantum yield for the formation of 17 (Φ rxn ) increased along the series 16cy > 16-Me > 16-H, but with an unexpected identical trend in

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“…233 Naphthyl cations 487 have been generated in the same way from enol triflate 486. 27,234 When the carbon ± carbon triple bond is further removed from the carbenium centre, the cyclisation becomes virtually impossible. 22,26 Another, barely studied, type of cations with a triple carbon ± carbon bond, namely the alkynyl cations R ± C:C + , should also be mentioned.…”

Section: Alkynyl Carbocations With a Remote Triple Bondmentioning

confidence: 99%