Aldehydes, addition derivatives reactions

Villsmeier reaction on the dimethylacetal of methoxyacetaldehyde (141) with phosgene and dimethyIformamide affords the acrolein derivative, 142. Condensation of this with guanidine gives the pyrimidine, 143. (The enamine can be viewed as a latent aldehyde-the dimethylamino group is probably lost in the course of an addition elimination reaction with one of the guanidine groups.) This pyrimidine serves as starting material for sulfameter (111). ... 

Enynes 71 react with aldehydes 61 in the presence of the [Ni(COD)J/SIPr catalytic system to afford two distinct products 72 and 73 (Scheme 5.20) [20b], The enone 72 is derived from aldehyde addition with the alkyne moiety while the adduct 73 arises from the aldehyde addition with the alkene moiety. The product distribution is dependent on the substituent on either the alkyne or alkene moieties. The reaction between 71 and ketones 74 led to the unprecedented formation of pyrans 75 (Scheme 5.20). The reaction showed to be highly regioselective in aU the cases, the carbonyl carbon was bound to the olefin. 

The reaction of these aldehydes, derived from periodate oxidation, with carbonyl reagents has also been investigated. Studies 147 148 were made on oxidized laminarin, a (1 —> 3)-linked polysaccharide, in which only the terminal residues had been oxidized. The addition of phenylhydrazine acetate detached the remainder of the terminal residue as glyoxal phenyl-osazone. When the aldehydic compounds derived from the periodate oxidation of raffinose and trehalose818a were reacted with p-nitrophenylhydrazine, the authors were surprised to find that one molecule of oxidized raffinose, containing six aldehydic functions, reacts with only three molecules of the reagent, and that the four aldehydic functions of the oxidized trehalose molecule react with only two. The reactions of periodate-oxidized carbo-... 

Dihydro derivatives are readily formed in reactions with aldehydes and ketones, and aldehyde addition products can be dehydrogenated to the fully conjugated heterocycles <1981RCR816, 1995AQ151>. In a new procedure, palladium iodide-catalyzed carbonylation of 1,8-naphthalenediamine 918 gave 2(l//)-perimidinone 921 in 91% yield <2004JOC4741>. 

The three-component method is applicable to the synthesis of various C(6)- or C(7)-functionalized PGs. Scheme 11 illustrates the tandem conjugate addition-aldol reaction that affords 7-hydroxy-PGE derivatives (18). Both saturated and unsaturated C7 aldehydes can be used as a side-chain units. The aldol adducts can be transformed to naturally occurring PGs (5a, 19) and, more importantly, to a variety of analogues such as tumor-suppressing A7-PGA, (20) or 7-fluoro-PGI2, a stabilized prostacyclin (21). The unique cellular behavior displayed by A7-PGA methyl ester is well correlated to its chemical reaction with thiols (20). 

In 1997, Kobayashi and colleagues reported the first truly catalytic enantioselective Mannich-type reactions of aldimines 24 with silyl enolates 37 using a novel chiral zirconium catalyst 38 prepared from zirconium (IV) fert-butoxide, 2 equivalents of (R)-6,6 -dibromo-l,l -bi-2-naphthol, and N-methylimidazole (Scheme 13) [27, 28], In addition to imines derived from aromatic aldehydes, those derived from heterocyclic aldehydes also worked well in this reaction, and good to high yields and enantiomeric excess were obtained. The hydroxy group of the 2-hydroxyphenylimine moiety, which coordinates to the zirconium as a bidentate ligand, is essential to obtain high selectivity in this method. 

The Homer-Emmons addition of dialkyl carboalkoxymethylenephosphonates to aldehydes [22] has been widely used to generate a,p-unsaturated esters which, in turn, can be reduced to allylic alcohols. Under the original conditions of the Homer-Emmons reaction, the stereochemistry of the oc,(3-unsaturated ester is predominantly trans and therefore the trans allylic alcohol is obtained upon reduction. Still and Gennari have introduced an important modification of the Homer-Emmons reaction, which shifts the stereochemistry of the a,[i-unsaturated ester to predominantly cis [23], Diisobutylaluminum hydride (DIBAL) has frequently been used for reduction of the alkoxycarbonyl to the primary alcohol functionality. The aldehyde needed for reaction with the Homer-Emmons reagent may be derived via Swern oxidation [24] of a primary alcohol. The net result is that one frequently sees the reaction sequence shown in Eq. 6A. 1 used for the net preparation of 3E and 3Z allylic alcohols. 

Optically active amino thiocyanate derivatives of (—)-norephedrine [e.g. (44)] have been found to act as effective aprotic ligands for enantioselective addition of diethylzinc to aldehydes.115 This reaction has provided optically active secondary alcohols with ee up to 96%. 

Germenes react with various reagents as shown in Scheme 20le,lp 51. For example, addition of methanol affords a methoxygermane. In the reactions with ketones and aldehydes oxagermetane derivatives are obtained. The reactions of a,/ -unsaturated aldehydes and ketones afford [4+2]cycloadducts. These reactions proceed regiospecifically, according to the Ges+=Cs polarity. 

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