Aldehydes orthoformate

Additionally, Grignard reagent reacts with an alkyl orthoformate to form an acetal which is then hydrolyzed to the corresponding aldehyde usiag dilute acid. 

Condensation. Depending on the reaction conditions, a variety of condensation products are obtained from the reaction of aromatic amines with aldehydes, ketones, acetals, and orthoformates. 

On the other hand, 1,1,1-trisubstituted alkanes behave similarly to aldehydes, yielding pyrjdium salts (128) with identical substituents in positions 2 and 6. Thus, Dorofeenko and co-workers condensed 2 moles of acetophenone with 1 mole of benzotrichloride in the presence of perchloric acid obtaining 2,4,6-triphenjdpjTylium perchlorate with 1 mole of ethyl orthoformate, they obtained 2,6-diphenyl-pyrylium perchlorate (57) from o-hydroxyacetophenone, ortho-formic ester and perchloric acid, 4-ethoxybenzopyrylium perchlorate was formed. 

The methiodide and ethiodide of 4-methylcinnoline possess methyl groups which condense easily with aldehydes, and even with ethyl orthoformate,to give polymethine derivatives. These reactions, particularly that with the ortho ester, suggest that the salts have structure 55 (R = Me or Et, R = Me). The methiodide of 3-methylcinnoline also reacts with aldehydes, although more slowly, but no reaction with ethyl orthoformate has been reported. Although 55 (R = Me) appears to be the most likely structure for the product, the 4-methyl group may direct the quatemization on and,... 

A completely different concept13 makes use of a highly reduced bilane 5 which is oxidatively cyclized to an isobacteriochlorin 6 with copper(II) acetate. The ring closure is initiated by ester cleavage with trifluoroacetic acid and decarboxylative formylation with trimethyl orthoformate to yield a dialdehyde. One of the aldehyde functions forms the desired methine bridge whereas the other is lost during cyclization. 

Aldehydes can be obtained by reaction of Grignard reagents with triethyl orthoformate. The addition step is preceded by elimination of one of the alkoxy groups to generate an electrophilic oxonium ion. The elimination is promoted by the magnesium ion acting as a Lewis acid.93 The acetals formed by the addition are stable to the reaction conditions, but are hydrolyzed to aldehydes by aqueous acid. 

The addition of Grignard reagents to aldehydes, ketones, and esters is the basis for the synthesis of a wide variety of alcohols, and several examples are given in Scheme 7.3. Primary alcohols can be made from formaldehyde (Entry 1) or, with addition of two carbons, from ethylene oxide (Entry 2). Secondary alcohols are obtained from aldehydes (Entries 3 to 6) or formate esters (Entry 7). Tertiary alcohols can be made from esters (Entries 8 and 9) or ketones (Entry 10). Lactones give diols (Entry 11). Aldehydes can be prepared from trialkyl orthoformate esters (Entries 12 and 13). Ketones can be made from nitriles (Entries 14 and 15), pyridine-2-thiol esters (Entry 16), N-methoxy-A-methyl carboxamides (Entries 17 and 18), or anhydrides (Entry 19). Carboxylic acids are available by reaction with C02 (Entries 20 to 22). Amines can be prepared from imines (Entry 23). Two-step procedures that involve formation and dehydration of alcohols provide routes to certain alkenes (Entries 24 and 25). 

The fact that reaction can be made to go with (25), but not with the simple R OH, is due to the ASe (c/ p. 36) value for the former being more favourable than that for the latter, which involves a decrease in the number of molecules on going from starting material to product. Both aldehydes and ketones that are otherwise difficult to convert into acetals may often be transformed by use of orthoesters, e.g. HC(OEt)3, triethoxymethane ( ethyl orthoformate ), with NH Cl as catalyst. 

Grignard reagents can also act as sources of negative carbon in displacement reactions, e.g. in the synthetically useful reaction with triethoxymethane (ethyl orthoformate, 58) to yield acetals (59) and, subsequently, their parent aldehydes (60) ... 

In addition to aldehydes and a-diketones, a-ketoesters can also be used in the domino process, as shown by Tietze and coworkers [396]. Reaction of methyl pyruvate 2-791 with dimethylbarbituric acid (2-747) and the enol ether 2-792 in the presence of trimethyl orthoformate (TMOF) and a catalytic amount of EDDA gave the cycloadduct 2-793 in 84% yield (Scheme 2.176). 

Aldehydes and ketones have been protected as acetals and dioxolanes using orthoformates, 1,2-ethanedithiol or 2,2-dimethyl-l,3-dioxolane by Hamelin and coworkers. This acid-catalyzed reaction proceeds in the presence of p-toluenesulfonic acid (p-TsOH) or KSF clay under solvent-free conditions (Scheme 6.2). The yields ob-... 

A big problem in asymmetric hydroformylation is that the chiral aldehyde products may be unstable and may undergo racemization during the reaction. This problem is even more serious for the Pt catalyst systems, which are usually plagued by slow reaction rates. Stille et al.121 tackled this problem by using triethyl orthoformate to trap the aldehyde products as their diethyl acetals and consequently increased the product ee values significantly. 

For instance, 2-methylpropene reacted with acetic acid at 18°C in the presence of Al-bentonite to form the ester product (75). Ion-exchanged bentonites are also efficient catalysts for formation of ketals from aldehydes or ketones. Cyclohexanone reacted with methanol in the presence of Al-bentonite at room temperature to give 33% yield of dimethyl ketal after 30 min of reaction time. On addition of the same clay to the mixture of cyclohexanone and trimethyl orthoformate at room-temperature, the exothermic reaction caused the liquid to boil and resulted in an almost quantitative yield of the dimethyl ketal in 5 min. When Na- instead of Al-bentonite is used, the same reaction did not take place (75). Solomon and Hawthorne (37) suggest that elimination reactions may have been involved in the geochemical transformation of lipid and other organic sediments into petroleum deposits. 

Using the optimized system for the two-component reaction, the same group [89] tested the three-component reaction, starting from an aldehyde, an amine and a phosphite (Scheme 42). An orthoester (trialkyl orthoformate, methyl or ethyl) was added to remove the formed water and to promote the imine formation, which was beneficial for the reaction however, these trials afforded maximally 49% yield due to the low conversions and low selectivities towards the desired aminophosphonates. 

Synthesis of l-hydroxy-3-oxyimidazolines from a-hydroxylaminooximes has been reviewed " . Therefore, in the present work it will be described very briefly. In general, the reaction of oximes 136 with aldehydes, ketone or triethyl orthoformate leads to imidazolines 137 or 138, respectively (equation 60). 

The behaviour of the ruthenium catalysts is quite different from that previously reported for cobalt carbonyl catalysts, which give a mixture of aldehydes and their acetals by formylation of the alkyl group of the orthoformate (19). The activity of rhodium catalysts, with and without iodide promoters,is limited to the first step of the hydrogenation to diethoxymethane and to a simple carbonylation or formylation of the ethyl groups to propionates and propionaldehyde derivatives (20). 

The use of aldehyde derivatives serves in lieu of the carboalkoxy group in cyclization reactions. The oxime 473, when allowed to react with triethyl orthoformate, gives the -oxide 474 (Equation 177) <1996H(43)389>. 

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