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Synthetic and mechanistic investigations on the rearrangement of 2,3-unsaturated 1,4-bis(alkylidene)carbenes to enediynes

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Title Synthetic and mechanistic investigations on the rearrangement of 2,3-unsaturated 1,4-bis(alkylidene)carbenes to enediynes
 
Creator SAHU, BICHISMITA
MURUGANANTHAM, RAJENDRAN
NAMBOOTHIRI, IRISHI NN
 
Subject chromatography
synthesis
quenching
toluene
 
Description 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
(CBr4, Ph3P, 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 N2, an alternative pathway, involving the vicinal elimination of HBr to afford an intermediate bromoalkyne and its subsequent
metal-halogen exchange and protonation during workup, exists for the bis(dibromoalkylidenes). However, our deuterium-
labeling experiments with a model substrate, deuterated p-methoxybenzylidene dibromide, established the predominance of the alkylidenecarbenes, generated in situ by
metal-halogen exchange and elimination, for this substrate and, by analogy, for the tetrabromides as well. The scope of this novel methodology was extended to the synthesis of various heteroatom-based (S, Se, and P) enediynes by quenching the acetylides with suitable electrophiles.
 
Publisher Wiley-VCH Verlag GmbH & Co. KGaA,
 
Date 2009-02-14T17:05:21Z
2011-11-25T16:52:54Z
2011-12-26T13:05:50Z
2011-12-27T05:53:44Z
2009-02-14T17:05:21Z
2011-11-25T16:52:54Z
2011-12-26T13:05:50Z
2011-12-27T05:53:44Z
2007
 
Type Article
 
Identifier European Journal of Inorganic Chemistry 2007(15), 2477–2489
10.1002/ejoc.200601137
1434-1948
http://hdl.handle.net/10054/645
http://dspace.library.iitb.ac.in/xmlui/handle/10054/645
 
Language en