Phosphine catalysts carbonates, asymmetric allylic

The asymmetric allylic substitution reaction of Morita-Baylis-Hillman carbonates (226) with diphenyl phosphite in the presence of chiral multifunctional thiourea-phosphine catalyst (228) provided allylic phosphites (227) in high yields and with excellent enantioselectivities (Scheme 76). 

Asymmetric allylation of carbon nucleophiles has been carried out extensively using Pd catalysts coordinated by various chiral phosphine ligands and even with nitrogen ligands, and ee > 90% has been achieved in several cases. However, in most cases, a high ee has been achieved only with the l,3-diaryl-substitiitcd allylic compounds 217, and the synthetic usefulness of the reaction is limited. Therefore, only references are cited[24,133]. 

Asymmetric allylic amination of allylic carbonates, prepared from racemic MBH adducts, proceeds in the presence of the Pd catalyst chiral diamino-phosphine oxide (DIAPHOX) (292) and BSA to afford the corresponding chiral aza-MBH adduct derivatives 293 in excellent yield with up to 99% ee. The cyclic reaction products could be converted into various synthetically useful compounds, such as chiral cyclic p-amino acids (Scheme 3.119). ... 

In 2010, Wang and co-workers [142] introduced phosphine oxides as nucleophiles to the asymmetric allylic substitution of BH carbonates. With quinidine as catalyst, the reaction proceeded smoothly to approach optically active allylic diaryl phosphine oxides in modest to good yields and enantioselectivities. A subsequent study showed that an additive was cmcial to the reaction with dialkyl phosphine oxides for example, excellent enantioselectivity was afforded with Na2C03 as the additive while a racemic product formed with NaOH as the additive [143]. 

The introduction of the activated allylic bromides and Morita-Baylis-HiUman acetates and carbonates pioneered the development of a number of phosphine-catalyzed reactions in subsequent years [45]. Interestingly, the asymmetric variant of this type of transformation only appeared in the literature seven years later. In 2010, Tang, Zhou, and coworkers disclosed a highly enantioselective intramolecular ylide [3-1-2] annulation using spirobiindane-based phosphine catalyst 31 (Scheme 20.27). BINAP was found inactive in this reaction even at an elevated temperature (70°C). Notably, both optically active benzobicyclo[4.3.0] compounds 32 and 32 with three continuous stereogenic centers could be obtained as major products in high yields and stereoselectivities just by a choice of an additive [Ti(OPr )4], which can block the isomerization of the double bond [46]. 

A variation on this asymmetric catalytic allylation scheme employed (3-diketones or (3-keto ester nucleophiles with allyl ethers and a palladium-DIOP catalyst.434 The chiral center generated is now one carbon removed from the allyl ligand. As a result, somewhat lower optical yields were observed (-10% equation 353). A variety of chiral phosphines were evaluated in the cyclization of (3-keto esters. Optical yields up to 48% were measured in these reactions435... 

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