New Synthetic Developments
Lee and Richardson have disclosed that it is entirely feasible to cyclopentannulate silyl enol ethers in a one-pot two-step process. For example, condensation of 1 with the readily available stannane 2 in the presence of trimethylsilyl triflate leads to an adduct that cyclizes to 3 on subsequent exposure to titanium tetrachloride . This new strategy is notable in that a doubly functionalized product results. 1,2-Bis(trimethylsilyloxy)cyclopentene (4) condenses with chloride 5 in the presence of anhydrous zinc chloride to give a 1:1 mixture of 6 and 7 . The first relevant point is that alkylation proceeds without annihilation of the allylsilane moiety. Consequently, this functionality is available for subsequent ring closure as illustrated by the independent conversion of 6 and 7 to 8 and 9, respectively, when treated with ethylaluminum dichloride.
KeywordsRing Expansion Diazo Ketone Synthetic Development Anhydrous Zinc Chloride Silyl Enol Ether
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