Rhodium carbenoid mediated cyclisations. Part 2. Synthesis of cyclic ethers
Alkylation of the dianion of methyl acetoacetate with the t-butyldimethylsilyl protected α,ω-halogeno alcohols (1)–(9) gives the β-keto esters (1) which are converted into the diazo alcohols (3) by diazo transfer and desilylation. Rhodium carbenoid cyclisation of the diazo alcohols (3b–d) gives the 7-membered ethers (11)–(13) in good yield. The 8-membered ether (14) is formed in only modest yield from the diazo alcohol (3e), but cyclisation of the diazo alcohol (3f) to the 10-membered ether (15) was not successful.