Aromatic acetals

CH2CO via rearrangement from a methyl ketone or an aromatic acetate or an aryl-NHCOCHj group... 

Jung and Maderna have reported the microwave-assisted allylation of acetals with allyltrimethylsilane in the presence of copper(I) bromide as promoter (Scheme 6.77b) [162]. Stoichiometric amounts of copper(I) bromide are required and the reaction works best with aromatic acetals free from strongly electron-withdrawing substituents on the aromatic ring. 

In addition, iodine snccessfnlly catalyzed the electrophilic snbstitntion reaction of indoles with aldehydes and ketones to bis(indonyl)methanes [225], the deprotection of aromatic acetates [226], esterifications [227], transesterifications [227], the chemoselective thioacetalization of carbon functions [228], the addition of mercaptans to a,P-nnsatnrated carboxylic acids [229], the imino-Diels-Alder reaction [230], the synthesis of iV-Boc protected amines [231], the preparation of alkynyl sngars from D-glycals [232], the preparation of methyl bisnlfate [233], and the synthesis of P-acetamido ketones from aromatic aldehydes, enolizable ketones or ketoesters and acetonitrile [234],... 

Azzena and colleagues have shown the [l,2]-Wittig-type rearrangement of aromatic acetals 55 induced by reductive electron transfer with lithium to give 56 (equation 30) , which was originally discovered by Schlenk and Bergmann in 1928 (with sodium). ... 

Krishnaveni NS, Surendra K, Reddy MA, Nageswar YVD, Rao KR (2003) Highly efficient deprotection of aromatic acetals under neutral conditions using beta-cyclodextrin in water. J Org Chem 68 2018-2019... 

M-42 ch2co (Methyl ketone (Aromatic acetate, Ar-NHCO-CH3 ... 

The dienone-phenol rearrangement of androsta-l,4,6-trien-3,ll,17-trione has been shown to lead to two major products, the AB-aromatic acetate (180 X = O) and the corresponding lla-ol (180 X = a-OH,H). Oxidation of the naphthol (180 ... 

Mansson P (1982) Selective deacetylation of aromatic acetates by aminolysis Tetrahedron Lett 23 1845-1846... 

Ramesh C, Mahender G, Ravindranath N, Das B (2003) A Mild, Highly Selective and Remarkably Easy Procedure for Deprotection of Aromatic Acetates Using Ammonium Acetate as a Neutral Catalyst in Aqueous Medium. Tetrahedron 59 1049... 

Aromatic acetals can be converted in 63-87 % yield to a-allylbenzylbromides by use of allyltrimethylsilane and a catalytic amount of SnBr2 in combination with excess acetyl bromide (Eq. 14) [23]. This reaction works equally well with SnCl2 and acetyl chloride to yield the corresponding a-allylbenzyl chlorides. The Friedel-Crafts allyla-tion of anisole with ally lie bromides catalyzed by SnBr2 has also been reported (Eq. 15) [24]. 

Carbonyls and acetals are converted to 1,3-dithianes and -dithiolanes upon treatment with 2-stanna-l,3-dithianes and -dithiolanes under catalysis by organotin tri-flates [147]. In these competition reactions, various types of carbonyl and acetal are differentiated. Aldehydes react preferentially over ketones (Eq. 104), but the preference is completely reversed in the competition reactions between the corresponding acetals and ketals (Eq. 105). The reactivity of aliphatic aldehydes is greater than that of the acetals of aliphatic aldehydes and ketones. Conversely, an aromatic acetal is... 

Benzylic acetate in erythro forms of /1-0-4 structures of syringyl ether type 2.29 Aromatic acetate... 

Supporting these arguments by analogy is the recent work of Kreevoy and Taft (5), in which aromatic acetals were found to hydrolyze some 40 to 800 times faster than aliphatic acetals. 

In the presence of excess acetyl halide and a tin(II) catalyst aromatic acetals react with allyltrimethylsilane to give a-allylbenzyl halides in good yield by double substitution of the acetal alkoxy groups (Scheme 10.127) [365]. The indium-catalyzed tandem reaction using a hydrosilane-allylsilane system enables deoxygenative allylation of aromatic ketones [366]. 

Bi(N03)3 5H20, CH2CI2, 76-98% yield. This method works for ketals and acetals that can delocalize a positive charge such as aromatic acetals. ... 

Decaborane in aqueous THF, >92% yield. The method only works for acetals that are electron-rich. Aromatic acetals with electron withdrawing groups fail to react thus providing some chemoselectivity. Decaborane can also be used for the formation of dimethyl acetals. 

This paper is devoted to the acylation in liquid phase of phenol and anisole by aromatic acetates. Reaction mechanisms are presented and the effect of the solvent polarity which is known to play an important role on the rate and on the selectivity of zeolite catalysed reactions... 

The rate of anisole acylation depended on the acetate (Table 2). Initially it was about 1.5 times greater with p-tolyl acetate and with 2-methoxyphenyl acetate than with phenyl acetate, slightly lower with 2-methoxyhydroquinone diacetate, 2.5 times lower with the hydroquinone diacetate and very low with 2,4,6-trimethylphenyl acetate. The low reactivity of this latter acetate can be related to limitations in the rate of diffusion of this bulky compound in the BEA zeolite pores. Furthermore, a greater reactivity of this acetate was found with HFAU zeolites whose pore size is greater. Curiously, with hydroquinone diacetate (but not with the 2-methoxyhydroquinone acetate), there was a quasi immediate deactivation. We are carrying out additional experiments so as to understand how the reactivity of aromatic acetates changes with their nature and the zeolite acidity and porosity. 

Under mild conditions (liquid phase, 160°C) HBEA zeolites can catalyse the acylation of phenol with phenyl acetate. High selectivity to p-hydroxyacetophenone is obtained by using sulfolane as a solvent, which can be explained by a better dissociation of phenyl acetate into acylium ions due to a solvation effect. However a competition between sulfolane and phenyl acetate for adsorption on the active acid sites is also demonstrated. A preliminary investigation of the effect of the acylating agent shows that generally, donor groups in aromatic acetates have a positive effect on the rate of acylation provided they do not block the access of the acetate to the acid sites of the zeolite pores. 

Methyl vinyl ketone. 6-Methyl-2-vinylpyridine. Vinyl carbomethoxymethyl ketone. AROMATIZATION Acetic anhydride-Phosphoric acid. Hydrobromic acid. Sulfuric acid. 

Chlorinated aromatics - Acetic acid methyl chloride. 

Homoallylic alcohols were directly prepared from aromatic acetals and dioxolanes (> 80%) using a Barbier-type allylation, Zn/allyl bromide/NH4Cl, in the presence of j3-CD in water at 50 °C (Figure 4.8). The synthesis of enantiomerically enriched homoallylic alcohols is an important goal in organic synthesis. An enantioselective metal-mediated allylation of substitnted benzaldehydes with jS-CD was achieved. The reaction proceeds in short reaction times (Ih) at room temperatnre. The homoallylic alcohols are obtained in moderate yields with up to 93% enantioexcess. 

K. Surendra, N. S. Krishnaveni, K. R. Rao, Direct Barbier-type allylation of aromatic acetals and dioxolanes in the presence of )S-cyclodextrin in water. Tetrahedron Lett, 2006, 47, 2133-2136. 

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