[4+2] Cycloaddition of 1,3-dienes to glycolaldehyde derivatives, leading to 5,6-dihydro-2H-pyrans, was effected by high pressure (10 kbar) in the presence of Eu(fod)3 (2%). Enantioselective version of the reaction was also studied.
The high-pressure [4+2]cycloaddition of 1-methoxybuta-1,3-diene to the glycolaldehyde-derived heterodienophiles, catalyzed by chiral metallosalen complexes
A high-pressure (ca. 10 kbar) reaction of 1-methoxybuta-1,3-diene 1 with variously O-protected glycolaldehydes 2, catalyzed by the chiral (salen)Cr(III)Cl 4a–d and 5 or (salen)Co(II) 6a–f and 7 complexes, has been studied. The best results were obtained for tert-butyldimethylsilyloxyacetaldehyde 2a. The reaction afforded, in good yield (up to 90%) and with very good diastereoselectivity (up to 92%)
The enantioselective high-pressure Diels–Alder reaction of 1-methoxybuta-1,3-diene with tert-butyldimethylsilyloxyacetaldehyde catalyzed by (salen)Co(II) and (salen)Cr(III)Cl complexes
reaction of 1-methoxybuta-1,3-diene (1) with tert-butyldimethylsilyloxyacetaldehyde (2), catalyzed by the chiral (salen)Co(II) 4 or (salen)Cr(III)Cl 5 complexes, has been studied. We found that the reaction afforded, in good yield (up to 90%) and both with very good diastereoselectivity (up to 92%) and enantioselectivity (up to 94% ee), the [4 + 2]cycloadducts 3, which are compounds of significant synthetic
Even moderately nucleophilic dienes react with simple aldehydes in the presence of a new Cr(III) catalyst in a hetero-Diels-Alder reaction [Eq. (1)]. Tetrahydropyranyl products with up to three stereogenic centers are generated in near-perfect diastereoselectivities and with greater than 90 % ee (99 % ee for the example shown). TBAF=tetrabutylammonium fluoride; TBS=tert-butyldimethylsilyl; TES=triethylsilyl.
AN EFFICIENT, HIGHLY DIASTEREO- AND ENANTIOSELECTIVE HETERO-DIELS-ALDER CATALYST. PREPARATION OF (2S,6R)-6-(tert-BUTYLDIMETHYL-SILYLOXYMETHYL)-2-METHOXY-2,5-DIHYDROPYRAN
作者:Chavez, David E.、Jacobsen, Eric N.、Grabowski, E. J. J.、Kubryk, Michele