Chiral auxiliary also menthol-derived

The Diels-Alder reaction of simple alkoxy alkenylcarbene complexes leads to mixtures of endo and exo cycloadducts, with the endo isomer generally being the major one [96,97]. Asymmetric examples of endo Diels-Alder reactions have also been reported by the use of chiral auxiliaries both on the carbene complex and the diene. Thus, the reaction of cyclopentadiene with chiral alkenylcarbene complexes derived from (-)-menthol proceeds to afford a 4 1... 

For acrylates, or type I reagents, applied in asymmetric Diels-Alder reactions, several chiral auxiliaries such as menthol derivatives, camphor derivatives,16,3 and oxazolidinones4 are available. Carbohydrate compounds have also been reported as chiral auxiliaries in a recent publication, although the stereoselectivity was not good.5 Here are examples in which asymmetric Diels-... 

A satisfactory result was obtained with the ligand 4 [43], which was synthesized from neo-menthol and contains an equatorial cyclopentadienyl group. The enantioselectivity of the opening attained synthetically useful levels (97 3) and the isolated yields were reasonable. Complex 5 [44], incorporating a ligand derived from phenylmenthone, also performed well. An enantioselectivity of 96.5 3.5 was observed. Phenylmenthol has already been extensively and successfully used as a chiral auxiliary [45]. 

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