P-spiro salts

The use of chiral P-spiro salts 5-8 in a nitroaldol reaction was recently reported by the Ooi group (Table 29.1) [10]. The reaction proceeded in the presence of 5 mol% of the chiral tetraaminophosphonium salt and KO Bu (5 mol%). It was postulated that the nitroalkane would be deprotonated by triaminoiminophospho-rane I, which would be the actual catalyst generated in situ from 5-8 and a strong base, forming a chiral phosphonium nitronate complex. An acyclic transition state model II predicting the formation of the anti adduct was proposed in which the Si-face of the nitronate would be set up to approach the Re-face of the aldehyde without significant sterical hindrance (Scheme 29.5). 

Ooi has recently reported application of chiral P-spiro tetraaminophosphonium salt 37 as a catalyst for the highly enantio- and diasterioselective direct Henry reaction of a variety of aliphatic and aromatic aldehydes with nitroalkanes (Scheme 5.51) [92]. Addihon of the strong base KO Bu generates in situ the corresponding catalyhcally active triaminoiminophosphorane base A. Ensuing formation of a doubly hydrogen-bonded ion pair B positions the nitronate for stereoselective addition to the aldehyde. This catalyst system bears many similarities to guanidine base catalysis. 

The metal-free asymmetric amination of benzofuranones has been achieved using binol-derived P-spiro quaternary phosphonium salts as organocatalysts (Scheme 3.36) [34]. The amination reactions were carried out under mild conditions using (E)-dibenzyl diazene-l,2-dicarboxylate as the nitrogen source. After stirring for several days, outstanding yields of the aminated compounds were obtained. 

In case of p-hydroxybenzenediazoniutn salts, the carbopalladation of alkynes leads to the formation of a spiro[4.5]decatetraene (Experimental Procedure below), ... 

More recently, catal 4ic asymmetric allylations of imines and imine derivatives in aqueous media have been studied. An A-spiro C2-symmetrical chiral quaternary ammonium salt (5,5)-I-Br [(5,5)-P-Np-NAS-Br] has been evaluated in the allylation of glycine tert-Bu ester benzophenone Schiff base [Ph2C=NCH2COOCMe3] for synthesis of both natural and unnatural a-amino acids (Eq. 11.45). ... 

The use of ot,p-unsaturated aldehydes as Michael acceptors always represents a challenging situation because of the tendency of enals to undergo 1,2- rather than the desired 1,4- addition reaction. Moreover, working under phase-transfer catalysis conditions incorporates an additional element of difficulty, because of the propensity of enolizable enals to undergo self-condensation side reactions. For this reason, there are only a few examples reporting enantioselective Michael reactions with ot,p-unsaturated aldehydes as Michael acceptors under PTC conditions, both coming from the Maruoka research team and also both making use of chiral tV-spiro quaternary ammonium salts as catalysts. 

Spirit of glyceryl trinitrate. See Nitroglycerin Spirit of Hartshorn. See Ammonium hydroxide Spirit of nitrous ether. See Ethyl nitrite Spirit orange. See Solvent yellow 14 Spirits of salt. See Hydrochloric acid Spirits of turpentine. See Turpentine Spirits of wine. See Alcohol Spirit of trinitroglycerin. See Nitroglycerin Spirit of turpentine. See Turpentine Spiro (benzofuran-2(3H), 1 -(2) cyclohexene)-3,4 -dione, 7-chloro-2, 4,6-trimethoxy-6 -p-methyl-. See Griseofulvin Spiro [bicycio [3.1.1] heptane-2,2 -oxirane], 6,6-dimethyl-. See Epoxypinane Spiro [1,3-dioxane-5,2 (2H)-napthalene], hexahydro-2,5, 5 -trimethyl-. See Dimethyl hexahydronaphthyl dihydroxymethyl acetal Spirofior. See 3-Ethyl-2,4-dioxaspiro (5.5) undec-8-ene... 

Formal a-diarylmethylation of malonates was achieved through the development of a 1,6-selective conjugate addition-aromatization sequence with para-quinone methides as vinylogous electrophiles (Scheme 4) [8]. The driving force toward aromatization would make nucleophilic addition to the 8-position more thermodynamically favorable than addition to the p-position. Under solid-liquid biphasic conditions, the A-spiro chiral ammonium salt 5 appeared to be the most active and selective promoter. The electronic character of the aryl ester substituents on the malonate was linked to the stereochemical outcome, and introduction of a para-halophenyl group led to a significant decrease in the enantioselectivity. Based... 

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