Stereoselective arylation, allylic esters

Moreover, when these reactions were performed at higher temperatures ( rt), DKR could be achieved. This was first demonstrated for a-aryl UNCAs [192], but subsequently also for a-allcyl UNCAs [193]. Allyl alcohol was found to be the optimal nucleophile, allowing a variety of UNCAs to be resolved with high stereoselectivities (90-92% ee) and good yields (93-98%) [192]. The resulting allyl esters could be converted to the optically active a-amino acids via Pd-catalyzed deallylation (Table 8.12). 

According to these considerations, the authors have developed Pd-catalyzed 7-selective and stereoselective allyl-aryl coupling between allylic ester and arylboronic acids according to the general Scheme 7.10. 

Allylic esters are among the most versatile substrate in organic synthesis. They are popular substrates for many transition metal-catalyzed reactions, such as dihydroxylation, the Tsuji-Trost reaction, hydrogenation, and isomerization, inter alia In this context, the Heck arylation can be considered a privileged reaction for the formation of such esters in a regio- and stereoselective way. However, this transformation has been a challenging one due to the... 

Our first applications of this new method have allowed the successful regio- and stereoselective arylation of acyclic allylic esters and A -protected allylamine derivatives. As a consequence of the high synthetic value of the arylated products, they were applied in the total synthesis of several bioactive compounds. Starting from allyUc esters, the synthesis of kavalactones such as the yagonine (27), methysticin (28), and dehydromethysticine (29) was accomplished in a straightforward way. Additionally, the y-arylated allylamine derivatives were applied to the total synthesis of the bioactive compounds naftifine (68), abamine (75), abamine SG (77), cinacalcet hydrochloride (85), and alverine (91). 

Kim et al. have reported a facile one-pot stereoselective synthesis of ( )-cinnamyl alcohols 113 via the treatment of MBH adducts, derived from aryl aldehydes and ethyl acrylate, with TFA. However, a similar reaction of MBH adducts derived from aryl aldehydes and acrylonitriles with TFA gave the ( )-allyl alcohols 111 in low yields (Scheme 3.40). " Since Basavaiah s method works well for nitrile-containing adducts [for ( )-selective nitriles] and the trifluoroacetic acid method works well with ester-containing adducts [for ( )-selective esters], these two methods are considered to be complementary for the preparation of stereochemically defined cinnamyl alcohols. 

The zinc homoenolate undergoes copper-catalyzed allylation with allylic chlorides. The reaction is not only extremely Sn2 regioselective but stereoselective for 5-chiral allylic chlorides. Arylation and vinylation of the zinc homoenolates proceed in the presence of a palladium-phosphine complex. Similarly, palladium-catalyzed acylation reaction gives y-keto esters (eq 6). 

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