Trienylic esters, rearrangement

Iron(tricarbonyl) was employed to control the diastereofacial selectivity in the enolate Claisen rearrangement of some trienyhc esters. Trienylic esters 137 and 139 underwent successful enolate Claisen rearrangements to afford 141 when treated with 1.05-1.15 equiv. of KHMDS in THF with 23% HMPA as cosolvent and 1.2 equiv. of TBDMSCl as an internal silylating agent (equation 67). Compound 137 yielded carboxylic acid 141 in 70-80% as a single diastereomer, while the yield from compound 139 was 45-50%. TBDMSOTf was used as an internal silylating agent for esters 138 and 140. In contrast to the results obtained with 137 and 139, inseparable mixtures of diastereomers 142 and 143 were obtained in 85-95% yield. 

In the additions of acetylenedicarboxylic esters to the (penta-l,2,4-trienyl)phosphonic esters 484 (R = Me), both head-to-head and head-to-tail products are formed. The initial reaction is then followed by 1,5-sigmatropic rearrangements to give isomers of benzylic phosphonic diesters, 485 (R = Me) and 486 (R = Me). The trienyl phosphonic esters 487 simi-larly give rise to aromatic phosphonic diesters 488 . The ester 484 (R = Et, R = H) is reactive towards A-phenylphthalimide at room temperature, but the product is not the expected 489 but rather 490, which aromatized on chromatography over alumina . The same trienyl phosphonic diesters undergo Diels-Alder reactions with sulphur dioxide and yield sulpholene adducts 491 and... 

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