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5473278 
Journal Article 
Investigations of the stereoselectivity of the intramolecular Diels–Alder reaction of a spiculoic acid model system 
Crossman, JS; Perkins, MV 
2008 
1 
Tetrahedron
ISSN: 0040-4020 
64 
21 
4852-4867 
Model linear precursors to the spiculoic acids were prepared and underwent thermally induced IMDA reactions. The configuration of C5 in the stereotriad was found to dominate any inherent endo/exo selectivity of the IMDA reaction. The isomer (2E,5S)-20 underwent the IMDA to give the spiculoic acid stereochemistry in 84% yield and 94% ds. The required stereotriads were synthesised using stereoselective substrate-controlled aldol reactions; an anti-boron aldol reaction, controlled by the π-facial preference of (S)-2-benzoyloxypentan-3-one ((S)-27) led to (5R)-(22) and a syn-titanium aldol reaction, under the stereocontrol of a chiral N-acylthiazolidinethione (42) led to (5S)-(22). Chain extension using standard Wittig, HWE and ‘modified’ Julia olefinations installed the diene and dienophile components giving the linear precursors to the IMDA reactions. 
Intramolecular Diels–Alder reaction; Substrate-controlled aldol reaction; Spiculoic acids