Diels-Alder reaction of in-situ generated 2-methoxycarbonyl-p-quinone with D-glucose based dienes: A new approach to forskolin

Asymmetric Diels–Alder cycloadditions of d-erythrose 1,3-butadienes to achiral t-butyl 2H-azirine 3-carboxylate

“…Two D-erythrose butadienes 1a,b were prepared according to the literature 6,7 and combined with t-butyl 2H-azirine 3-carboxylate, obtained in situ from t-butyl a-azido acrylate; 9 the reaction occurs at 60°C. Two products were formed in each reaction in the same ratio.…”

“…The lack of interest in these dienes, namely as counterparts in Diels-Alder cycloadditions (DA), is probably due to the poor facial selectivity associated with DA thermal processes, although exceptions are known. 6,7 Nevertheless, a series of interesting compounds could be envisaged by functional group transformations (FGT) of these DA cycloadducts mainly in the field of sugars/aza-sugars. Therefore we attempted to better understand the facial selectivity of dienes 1 with dienophiles in order to improve the selectivity.…”

Diastereoselectivity in Diels-Alder Cycloadditions of Erythrose Benzylidene-acetal 1,3-Butadienes with Maleimides

“…In the past a high diastereotopicity was demonstrated in Diels-Alder reactions of these dienes with 2-methoxycarbonyl-p-benzoquinones. 1 In a previous study in our laboratory a complete chiral induction was also found in [4π+2π] cycloadditions of certain D-erythrose benzylidene-acetal 1,3-butadienes, having ether protection at C-5, with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), 2 Maleimide (3), and Nphenylmaleimide (4). The facial selectivities were moderate to good under elevated temperatures, and interestingly the topicity was reversed when the cycloadditions were carried out at 5 °C.…”

“…Small chiral synthons are becoming more and more appealing to synthetic chemists to build up target molecules possessing multistereogenic centers. We have been investigating the utility of D-erythrose 1,3-butadienes, such as 1 and 2, 1 as chiral counterparts in diastereoselective Diels-Alder cycloadditions. In the past a high diastereotopicity was demonstrated in Diels-Alder reactions of these dienes with 2-methoxycarbonyl-p-benzoquinones.…”

Can Diels–Alder Reactions Lead to trans‐Fused Products? A Computational Study of the Competitive [4+2] and [2+4] Cycloaddition of Dienes to α‐Aryl‐Substituted Cyclohexenones

“…The one‐step nature of DA reactions43–46 is a major aspect of this type of process and, although mandatory to the attainment of high degrees of stereocontrol, it somehow reduces the potential of the chemical transformation by not allowing the formation of trans ‐fused products 47. Experimental chemists have circumvented this limitation by epimerizing the cis junction obtained in DA reactions (Scheme ) 48–50. However, this approach suffers from important limitations as the products need to have a vicinal keto group to enable the epimerization and the thermodynamics of the products have to favor the trans isomer.…”