Formylation a-synthons

The Michael acldiQon of rutromethane to cyclopentenone clenvaQves is used for synthesis of prostaglandins fScheme 4 20 Here, the aruon of rutromethane is used as a formyl aruon synthon... 

The Michael addition of nitromethane to cyclopentenone derivatives is used for synthesis of prostaglandins (Scheme 4.20).158 Here, the anion of nitromethane is used as a formyl anion synthon. 

Phenylthio-l-trimethylsilylalkanes are easily prepared by the alkylation of (phenylthioXtrimethylsilyl)mcthane as shown in Scheme 10 [40], The treatment of (phenylthio)(trimethylsilyl)methane with butyllithium/tetramethylethylene-diamine (TMEDA) in hexane followed by the addition of alkyl halides or epoxides produces alkylation products which can be oxidized electrochemically to yield the acetals. Since acetals are readily hydrolyzed to aldehydes, (phenylthioXtrimethylsilyl)methane provides a synthon of the formyl anion. This is an alternative to the oxidative transformation of a-thiosilanes to aldehydes via Sila-Pummerer rearrangement under application of MCPBA as oxidant [40, 41]. 

Although various compounds are known to act as synthetic equivalents to the formyl anion synthon,12 the advantages that appear to be associated with the use of 2-TST warrant comment. First, 2-TST is a readily available, relatively cheap, and storable reagent second, it reacts promptly and stereoselectively with aldehydes under neutral conditions third, it gives high yields of products that are stable to isolation and purification and nevertheless can be readily transformed into aldehydes. 

On the other hand, when about 4 Fmol-1 of electricity is passed in the anodic oxidation of cr-thiomethylsilanes, both desilylation and desulfurization take place to give the corresponding acetals in good yields as follows. Since acetals are easily hydrolyzed to aldehydes, such an a-thiomethylsilane is a synthon of a formyl anion (equation 22). 

S. namaquense its structure is based on spectral study Several new syntheses of meserabrine have been reported. One uses a cinna-monitrile as a synthon, with introduction of a "formyl anion" at the S-position, followed by Robinson annelation and finally elaboration of the cyanomethyl side-chainA second employs an intramolecular ene cyclisation of an acylnitroso-olefin to a hydroxamic acid, reducible to a lactam. Then follows a series of simple steps (N-methylation, hydroxylation via bromohydrin formation, debromi-... 

Aldehyde synthesis. Aldehydes are obtained through alkylation under solid-liquid biphasic conditions followed by reduction with LiAlH4 and Hg(II)-promoted hydrolysis. Thus the bissulfonyl methanes are a formyl anion synthon. 

The versatility of CO as a synthon also stems from its ability to undergo insertion reactions into a variety of metal-heteroatom bonds. The migratory insertion of CO into transition metal-hydride bonds, while thermodynamically unfavorable, generates metal-formyl complexes M-C(0)H (Equation (19)), a few examples of which have been isolated independently. This reaction is assumed to be a key step in both the homogeneous and heterogeneous catalytic hydrogenation (i.e., reduction) of CO, including the Fischer-Tropsch synthesis of hydrocarbons and... 

Hence, (1) serves as a synthetic equivalent for the formyl anion synthon which adds to the aldehyde in a stereoselective manner, creating a new chiral hydroxymethylene center. The repetition of the first and second operational sequences above over six consecutive cycles with high levels of diastereoselectivity and chemical yields in each cycle provided a series of protected D-aldoses having up to nine carbons in the chain (eq 8). 

Two groups have reported the use of phenylthiomethyltrimethylsilane as a formyl anion synthon. Alkylation of the lithium anion may be accomplished in THF, or in hexane containing TMEDA. A distinct advantage of this formyl synthon is the ease of unmasking the aldehyde via a sila-Pummerer rearrangement (Scheme 6). However, as steric crowding about the intermediate sulphoxide... 

Formylation Reactions. DMF dialkyl acetals exhibit reactivity as a formyl cation synthon by introducing a C unit at many nucleophilic centers (e.g. at N, S, O, or CH). For example, DMF dimethyl acetal can be used instead of formic acid for conversion... 

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