Acyl compounds, addition

There has been recent interest in naphtho-fused dithiepines as chiral acyl anion equivalents, particularly since the starting dithiol 128 can be obtained in enan-tiomerically pure form (89TL2575). This is transformed using standard methods into the dithiepine 129, but showed only moderate diastereoselectivity in its addition to carbonyl compounds. On the other hand, as we have seen previously for other systems, formation of the 2-acyl compound 130 and reduction or addition of a Grignard reagent gave the products 131 with much better stereoselectivity (91JOC4467). 

Sulfoxides (R1—SO—R2), which are tricoordinate sulfur compounds, are chiral when R1 and R2 are different, and a-sulfmyl carbanions derived from optically active sulfoxides are known to retain the chirality. Therefore, these chiral carbanions usually give products which are rich in one diastereomer upon treatment with some prochiral reagents. Thus, optically active sulfoxides have been used as versatile reagents for asymmetric syntheses of many naturally occurring products116, since optically active a-sulfinyl carbanions can cause asymmetric induction in the C—C bond formation due to their close vicinity. In the following four subsections various reactions of a-sulfinyl carbanions are described (A) alkylation and acylation, (B) addition to unsaturated bonds such as C=0, C=N or C= N, (C) nucleophilic addition to a, /5-unsaturated sulfoxides, and (D) reactions of allylic sulfoxides. 

Halogenation of alkenyl organometallic compounds Addition of hydrogen halides to triple bonds Halogenation of alkynes or allenes Addition of alkyl halides to triple bonds Addition of acyl halides to triple bonds... 

C(l)-Acylation of the l,4-dihydro-277-pyrazino[2,TA]quinazoline-3,6-diones 57 (R4 = Me, Rz = Bn, CH2-C6H4-MeO-/>) by treatment with LHDMS at — 78 °C followed by addition of acyl chlorides resulted in the as- 1-acyl derivatives with de > 95% in good yield. Formation of the air-product was explained by equilibration through the anion formed by deprotonation at C-l. The 1-acyl compounds were unstable and easily retransformed into the starting 57 <1998TA249>. 

Tetra-0-acetyl-2-amino-2-deoxy- 3-D-glucopyranose Q.) (8) was treated with do-, tetra-, hexa-, and octadecanoyl (laur-oyl, myristoyl, palmytoyl, and stearoyl) chlorides in 2 1 chloroform-pyridine solution, to give the crystalline 1,3,4,6-tetra-0-acetyl-2-acylamino-2-deoxy- 3-D-glucopyranoses ( ) (9). In addition to the n-fatty acyl compounds , we also prepared the... 

Cobalt complexes derived from Schiff bases 388 catalyzed the hydroxyacylation of electron-deficient alkenes (Fig. 90) [431, 432]. Thus, methyl acrylate 387 reacted with aliphatic aldehydes 386 in the presence of 5 mol% of the in situ generated catalyst, molecular oxygen, and acetic anhydride to 2-acyloxy-4-oxoesters 389 in 56-77% yield. When acetic anhydride was omitted, the yields of products were lower and mixtures of the free hydroxy compounds and acylated compounds resulting from Tishchenko reactions were obtained. Electron-rich alkenes did not undergo the transformation, since the addition of the acyl radical is much slower. The acylcobalt species inserts oxygen instead and acts as an epoxidation catalyst. 

For the first time, inverse substrates provide a general method for the specific introduction of an acyl group into the trypsin active site without recourse to cation-containing acyl compounds. The preparation of various new acyl enzymes is expected to lead to the discovery of novel features of the enzymatic reaction mechanism. In addition, any desired reporter groups might be specifically introduced into the trypsin... 

The perhydroxyl anion, HOf, is a powerful nucleophile (see Chapter 3) and will attack substrates such as electron-deficient olefins (e.g. a,/ -unsaturated ketones) and aldehydes. The perhydroxyl anion is also of value in bleaching and product purification, particularly of natural products. In addition, it can be used to generate more powerful oxidants by mixing with electron-deficient acyl compounds (giving peroxyacids) or with nitriles (Figure 2.5). 

Through the oxidative addition of aldehydes, hydridoformyl and -acyl compounds are formed. Formaldehyde adds to the reactive complex, [Ir(PMe3) ]PF, to afford [HIr(CHO)(PMe3) ]PF. Cyclometallation of an aldehyde H—C bond results from treating RhCl(PPh3)3 with 8-quinolinecarboxaldehyde in CH2CI2 in 10 min to yield (95%) HRh(CRO)Cl(PPh3)2 (R = 8-carboxyquinoline). ... 

If the anodic oxidation of N-alkylanilines is performed in the presence of nucleophiles like enol ethers, nucleophilic substitution in the of-position to nitrogen by the enol ether can be observed in low yields. The electrophilic intermediate is the N-aryl iminium ion or the N-aryl imine after loss of two electrons and one or two protons. These intermediates add to the enol ether to give acetals (up to 26%) as addition products, or the first addition step is followed by an electrophilic aromatic substitution to form tetrahydroqui-nolines (13-39%) [47]. It should be noted at this point that better results for the nucleophilic a-substitution to nitrogen can be obtained with N,N-dialkylanilines (see next subsection). Optimum results, however, are obtained with N-acylated compounds via the intermediate N-acyl iminium ions (see Ref. 8). 

It is in the second step of the reaction that acyl compounds differ from aldehydes and ketones. The tetrahedral intermediate from an aldehyde or ketone gains a proton, and the result is addition. The tetrahedral intermediate from an acyl... 

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