Chapter 24: Problem 6
What sequence of reactions will produce the following product if starting with trimethylsilylacetylene and the appropriate two aryl iodides?
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Over the past several decades, chemists have developed a number of synthetic methodologies for the synthesis of steroid hormones. One of these, developed by Lutz Tietze at the Institut für Organische Chemie der Georg-August- Universität, Göttingen, Germany, used a double Heck reaction to create ring \(\mathbf{B}\) of the steroid nucleus. As shown in the following retrosynthetic analysis, a key intermediate in his synthesis is compound (1). Two Heck reaction disconnects of this intermediate give compounds (2) and (3). Compound (2) contains the aromatic ring that becomes ring A of estrone. Compound (3) contains the fused fiveand six-membered rings that become rings \(C\) and \(D\) of estrone. (a) Name the types of functional groups in estrone. (b) How many chiral centers are present in estrone? (c) Propose structural formulas for compounds (2) and (3). (d) Show how your proposals for compounds (2) and (3) can be converted to compound (1). (Note: In the course of developing this synthesis, Tietze discovered that vinylic bromides and iodides are more reactive in Heck reactions than are aryl bromides and iodides.) (e) In the course of the double Heck reactions, two new chiral centers are created. Assume in compound (3), the precursor to rings \(C\) and \(D\) of estrone, that the fusion of rings \(C\) and \(D\) is trans and that the angular methyl group is above the plane of the ring. Given this stereochemistry, predict the stereochemistry of compound (1) formed by the double Heck reaction. (f) To convert (1) to estrone, the tert-butyl ether on ring D must be converted to a ketone. How might this transformation be accomplished?
When the \(\mathrm{Pd}(0)\)-catalyzed reactions covered in this chapter are run with a slight pressure of carbon monoxide, a ketone is often created as the product. For example, the following Stille coupling conditions with added CO give the product shown. Write a mechanism for how this reaction could occur using the organometallic mechanistic steps introduced in this chapter, along with new steps that would be required in this transformation. Hint: CO can coordinate to \(\mathrm{Pd}\) and insert into \(\mathrm{Pd}-\mathrm{C}\) bonds.
Treatment of cyclohexene with iodobenzene under the conditions of the Heck reaction might be expected to give 1-phenylcyclohexene. The exclusive product, however, is 3-phenylcyclohexene. Account for the formation of this product.
The aryl diene undergoes sequential Heck reactions to give a product with the molecular formula \(\mathrm{C}_{15} \mathrm{H}_{18}\). Propose a structural formula for this product.
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