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Chapter 46 Suggested solutions for Chapter 46 433 the two dithioacetals work as d¹ reagents (acyl anion equivalents, p. 1256) by deprotonation This chemistry was used to make lation. Hydrolysis needs mercury, Hg(II) as described on p. 1255. the perfume cis-jasmone by R. A. Ellison and W. D. Woessner, J. Chem. Soc., Chem. Commun., 1972, 529. HgCl₂ S S S S S S S S H BuLi Li Mel Me BuLl RBr acetone Me product 5 S S S S S S S roblem 9 est a mechanism for this formation of a nine-membered ring. Warning! The weak base is not strong enough to form an enolate from the lactone. S S N weak hindered base 0 of the problem tricky sulfonium ylid rearrangement. solution base can do nothing to our sulfur compound so it must do something by itself - on at sulfur is the answer. Sulfur is a good soft nucleophile and allylic iodides are excellent iles. Now the weak base can remove a proton because the result is an enolate and a ylid as well. S S H :B S S 0 0 0 0 0 0 0 ylid is perfectly arranged for a [2,3]-sigmatropic rearrangement forming a nine-membered If the sulfur were removed by Raney nickel, we should have an with a trans (E-) alkene inside it. eleven-membered ring and this was the idea of E. Vedejs et al., J. Org. Chem., 1981, 46, 5452. [2,3]- sigmatropic S S Raney Ni rearrangement 0 0 0 0 0