The standard procedure for synthesizing a compound is the stepwise progress towarda

Chapter 7, Problem 7.28

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The standard procedure for synthesizing a compound is the stepwise progress towarda target molecule by forming individual bonds through single reactions. Typically, theproduct of each reaction is isolated and purified before the next reaction in the sequenceis carried out. One of the ways nature avoids this tedious practice of isolation and pu-rification is by the use of a domino sequence in which each new product is built on apreexisting one in stepwise fashion. A great example of a laboratory domino reaction isWilliam S. Johnsons elegant synthesis of the female hormone progesterone. Johnson firstconstructed the polyunsaturated monocyclic 3 alcohol (A) and then, in an acid-induceddomino reaction, formed compound B, which he then converted to progesterone. A remarkable feature of this synthesis is that compound A, which has only one stereo-center, gives compound B, which has five stereocenters, each with the same configurationas those in progesterone. We will return to the chemistry of Step 2 in Section 16.7 and tothe chemistry of Steps 3 and 4 in Chapter 19. In this problem, we focus on Step 1.(a) Assume that the domino reaction in Step 1 is initiated by protonation of the 3alcohol in compound A followed by loss of H2O to give a 3 carbocation. Show howthe series of reactions initiated by the formation of this cation gives compound B.(b) If you have access to a large enough set of molecular models or to a computermodeling program, build a model of progesterone and describe the conformationof each ring. There are two methyl groups and three hydrogen atoms at the set of