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Sigmatropic 1,2- and 1,3-acyl shifts in excited states: a novel, general protocol for the synthesis of tricyclopentanoids and protoilludanes

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Title Sigmatropic 1,2- and 1,3-acyl shifts in excited states: a novel, general protocol for the synthesis of tricyclopentanoids and protoilludanes
 
Creator SINGH, V
PORINCHU, M
 
Subject mediated cyclization reaction
linear triquinane synthesis
secondary mold metabolites
gamma-unsaturated ketones
ring cyclopropyl ketones
diels-alder reaction
armillaria-mellea
natural-products
antibacterial sesquiterpenoids
rearrangement approach
 
Description A novel and general approach for the synthesis of linearly fused cis:anti:cis tricyclopentanoids and protoilludane framework having fused four, six and five membered rings from common precursors has been delineated. Photochemical sigmatropic 1,2-acyl shift (or oxa-di-pi-methane rearrangement) and 1,3-acyl shift in annulated bicyclo[2.2.2]octenones are the key features of this approach. An efficient one step synthesis of epoxy ketones 15-17 via pi(4)s+pi(2)s cycloaddition of in situ generated cyclohexa-2,4-dienone 11 has been reported. Further transformation of 15-17 and their congeners to a variety of chromophoric systems 22-31 has been described. The structure and stereochemistry of annulated bicyclo[2.2.2]octenones 15-31 has been established through their high field H-1-NMR (300MHz), C-13-NMR, decoupling experiments and cosy spectra. Photochemical behaviour of selected chromophoric systems upon tripler (T-3) and singlet (S-1) excitations has been investigated. While triplet excitation (T-3) of 23, 24, 26-28, 30-32 and 35 led to formation of tetracyclic systems 38-47, the singlet excitation (S-1) of 23, 24, 27, 28, 29b; 31b, 36 and 55 furnished the protoilludanoids 56-63. Interestingly, 29b did not undergo 1,2-acyl shift upon tripler excitation, but it underwent 1,3-acyl shift upon singlet excitation to give 60. Cleavage of cyclopropane ring in some of the tetracyclic products has also been investigated. Reductive cleavage of 38, 44, 46 and 47 to tricyclic systems 50-53 has also been reported. Copyright (C) 1996 Elsevier Science Ltd
 
Publisher PERGAMON-ELSEVIER SCIENCE LTD
 
Date 2011-10-14T11:43:34Z
2011-12-15T09:16:20Z
2011-10-14T11:43:34Z
2011-12-15T09:16:20Z
1996
 
Type Review
 
Identifier TETRAHEDRON,52(20)7087-7126
0040-4020
http://dx.doi.org/10.1016/0040-4020(96)00329-8
http://dspace.library.iitb.ac.in/xmlui/handle/10054/13911
http://hdl.handle.net/100/3113
 
Language en