Allenol Ether Intermediates in the Synthesis of 1,7-Dioxaspiro[5.5]undec-4-enes and 1,6-Dioxaspiro[4.5]dec-3-enes
作者:Philip Kocieński、Richard Whitby
DOI:10.1055/s-1991-26640
日期:——
Sequential dialkylation of methoxyallene via the corresponding lithium derivatives gives 1,3-dialkylated methoxyallenes which undergo acid-catalysed ring closure to 1,7-dioxaspiro[5.5]undec-4-enes. Similarly, cyclic allenol ethers (2-vinylidenetetrahydropyrans) generated by rearrangement of 2-alkynyltetrahydropyrans cyclise on treatment with acid to give 1, 6-dioxaspiro[4.5]dec-3-enes.
2,3-Disubstituted oxepanes 3 and 4 were stereoselectively synthesized from methoxyallene (1) and iodide 2. The trans stereochemistry of diol 3 was established by NMR studies of the bicyclic precursor 10, while the cis stereochemistry of 4 was secured by using the highly diastereoselective reducing agent L-Selectride.