Course Meeting Times
Lecture: 2 sessions over 4 weeks, 1 hour / session
Labs: 2 sessions / week, 4 hours / session
5.13 Organic Chemistry II
This course provides students with a research-inspired laboratory experience in which students carry out a short synthetic sequence including a catalytic asymmetric cycloaddition reaction. The experiment provides students with experience with a variety of advanced techniques for carrying out organic reactions including the use of air-sensitive reagents, distillation, recrystallization, and column chromatography. Analytical techniques include the use of chiral GC for determination of enantiomeric purity.
The key reaction in the experiment is the asymmetric Diels-Alder reaction of cylcopentadience with methacrolein. In principle four stereoisomeric [4+2] cycloaddition products can result from this reaction, so both diastereoselectivity and enantioselectivity are involved in determining the outcome of the reaction.
|Dry and purify triethylamine by distillation and purify dibenzyl tartrate by trituration and recrystallization.
|Set up esterification of dibenzyl tartrate with 2,6-dimethoxybenzoyl chloride which then runs overnight at reflux. The teaching assistants will turn off the heat the following day for you and the reaction will be allowed to proceed at room temperature until the next laboratory period of your group.
|Work up the esterification reaction.
|Purify the product of the esterification reaction by column chromatography. Analysis of the product by proton NMR spectroscopy (spectrum can be run at the beginning of Day 5 if necessary).
|Set up the hydrogenolysis reaction which will then run over the weekend at room temperature. If necessary, the teaching assistants will add more hydrogen to your balloons on the day after you set up the reaction.
|Filter and concentrate the hydrogenolysis reaction mixture, and set up overnight drying of the diacid product under vacuum. The measurement of the melting point of the product and NMR analysis can be performed either at the beginning of Day 7 or on an “off day” for your group between Days 6 and 7.
|Generate the chiral CAB Lewis acid catalyst in situ and set up the Diels-Alder reaction to run overnight at low temperature. The teaching assistants will add additional dry ice to your cooling bath during the evening to extend the time that the reaction remains below -70 °C.
|Work up the Diels-Alder reaction and analyze the crude product by TLC and proton NMRspectroscopy.
|Purify the Diels-Alder product by column chromatography and separate the endo and exo cycloadducts.
|Analyze the Diels-Alder product by proton NMR spectroscopy and determine the enantiomeric ratio for the exo isomer by gas chromatography using a chiral GC column. This characterization can be completed on Day 11 if necessary.
|Extra time for completion of the experiment and checkout.