Microwave assisted Diels-Alder reaction between levoglucosenone and 9-substituted anthracenes

SAROTTI, A.M.; SPANEVELLO, R.A.; JOULLIÉ, M.M.; SUÁREZ, A.G.

WASHINGTON DC, EEUU

Otro; 4th Annual Summer School on Green Chemistry; 2006

  Paper is an important industrial material which is used in a wide variety of applications. An increasing demand of this material has forced to recycle waste paper into paper pulp . By doing this, great energy saving can be achieved and wood depletion from the forest could be avoided. Unfortunately, paper recycling has a limited number of turn over, due to the lower quality of product obtained in each cycle, but waste paper still constitute an important portion of biomass. As part of our program on the pyrolytic conversion of biomass into high value chemicals, we have been concerned with the synthetic application of levoglucosenone (1) as a chiral building block in the development of new tools for asymmetric synthesis. This bicyclic enone is the major product from the pyrolysis of cellulose or cellulose-containing material such as waste paper. Recently we have reported the design and synthesis of two alcohols derived from levoglucosenone and their use as chiral inductors in Diels-Alder reactions.  Cycloadditon of cyclopentadiene with the corresponding acrylate derivatives yielded the desire products with up to 98 % diastereoisomeric excess. These encouraging results obtained prompted us to design and synthesize new chiral auxiliaries starting from paper. The general synthetic approach is shown in Figure 1. The key step in the sequence is the Diels-Alder reaction between levoglucosenone and a 9-substituted anthracene, leading to the formation of two isomeric compounds: adducts ortho and meta. After testing the reaction under several experimental conditions, we found that the only way to obtain good yields was by using an excess of diene in refluxing toluene.    Eventhough the range of yields and selectivities were very good to excellent, the reaction times were very long (7 to 10 days). For that reason, and taking into account that microwave assisted Diels-Alder reactions are gaining increased importance, we decided to study the use of microwave irradiation to determine the effects on the yield and regioselectivity of the Diels-Alder reaction. Herein we discussed the results obtained in this study.