Following is an outline of a synthesis of bombykol, the sex attractant of the male silk- worm moth. Of the four stereoisomers possible for this conjugated diene, the 10-trans- 12-cis isomer shown here is over 106 times more potent as a sex attractant than any of the other three possible stereoisomers. H H ÓMe ÓMe trans 12 cis HO (3) ÓMe Bombykol C16H3,0 Show how this synthesis might be accomplished and explain how your proposed syn- thesis is stereoselective for the 10-trans-12-cis isomer.

Identify the expected major products of the following intramolecular Diels-Alder reaction. CH₂O O CH3O CH₂O OCH3 11 CH₂0 OCH3 En OCH3 CH3O +En IV A CH3O O V ? CH3O сноя Росто OCH3 OCH3 VI

Heating the following molecule in ethanol gave a major product with molecular formula C,H12 , which when treated with O3 followed by Me2S produced the diketone shown. Br CH3CH,OH 1. O3 C,H12 heat 2. Me,S (i) Deduce the structure of the product with molecular formula C,H12 from the information provided. Write an arrow formalism reaction mechanism to show how the compound with molecular formula C,H12 is formed. (ii) How would you perform the following transformation to obtain the final product as the MAJOR product. More than one step is needed. Show all the steps in your synthesis. Reaction mechanisms are not required. Br more than one step less than four steps OHC CHO

6. HO3S Synthesize the following compounds starting from benzene: H3C CH3 NH2 Br SO 3H H₂C CH3 Cl CH3

The reaction of butan-2-ol with concentrated aqueous HBr goes with partial racemization, giving more inversion than retention of configuration. Propose a mechanism that accounts for racemization with excess inversion

13. On treatment with nitrous acid (HNO2) these 4 isomers of 1 react differently. (a) Draw a mechanism for the reaction of each stereoisomer, and hence identify which stereoisomer gives which product A, B or C. (b) Draw the orbital interactions involved in the product-determining step for each reaction. A H B C To get you started: OH OH HNO2 1 NH2 NEN