Week 3 Discussion - Consider the Diels-Alder cycloaddition

Week Three Discussion

ORGANIC 2 DISCUSSION 3

1. Consider the Diels-Alder cycloaddition reaction below and complete parts (a)-(b) below.

(a) Draw the major regioisomer (or in other words, constitutional isomer) expected to form. Also, draw appropriate resonance structures to explain why only one constitutional isomer is expected to form. Discuss the interactions between the diene and dienophile that govern this constitutional isomer being the only one expected.

(b) Redraw the regioisomer from part (a) and show the appropriate stereochemistry using correct dash/wedge notation expected for the major product. Discuss if this is the endo or exo diastereomer and draw a transition-state intermediate to help illustrate why this diastereomer is favored. Also, discuss if you believe this diastereomer is chiral or achiral. If it is chiral, also discuss if you think it will be formed as an equal mixture of two enantiomers (known as racemic).

2. Consider the reaction below and complete parts (a)-(c): (Complete a to c in the next pages)

(a) When the molecule below is treated with HBr at high temperatures, the 1,2-addition product predominates, rather than the 1,4-adduct. Draw this product and explain this result. Use appropriate resonance structures to illustrate.

(b) Indicate if this product is (i) achiral, (ii) chiral and racemic, or (iii) chiral, non-racemic. Discuss how you know this to be true.

(c) Is this product the thermodynamic product or kinetic product? Discuss what led you to this answer.

3. Using the carbon sources provided and any other necessary reagents needed, propose a viable synthesis for the product shown. Your synthesis must include a Diels-Alder reaction. For each step in your synthesis be sure to show the reagents/conditions necessary for that step and also draw the major product expected for each step leading to the product. You will also need to use reactions discussed in previous chapters as well.