With carbonyl derivatives

Even when deactivated by nitro substitution on C-5, the 2-aminothiazoles still undergo diazotization (35, 338-340). As with carbonyl derivatives (Section III.2.B), competition may occur between N nucleophilic reactivity and nitrosation of the 5-position when it is unsubstituted (341-344). 

Furthermore, they react with carbonyl derivatives such as acetone and benzaldehyde to give selenohydrazones identical to those prepared from the condensation of selenosemicarbazones with an a-halocarbonyl compound. 

The 5-lithium derivative (90) obtained upon metalation of 2-tert-butyl-selenophene ether (89) was treated either with alkyl halides or with carbonyl derivatives (Scheme 8). 

Cyclodditions to Carbonyl Derivatives. Electrophilic transient carbenes are known to react with carbonyl derivatives through the oxygen lone pair to give carbonyl ylides 26.43 These 1,3-dipolar species are usually characterized by [3 + 2]-cycloaddition reactions or can even be isolated44 a small amount of the corresponding oxiranes is sometimes obtained.433,45 To date, no reaction of transient nucleophilic carbenes with carbonyl derivatives has been reported. 

In practice, the original method had its limitations since one equivalent of TiCl4 had to be used and usually led to the cyclic derivatives. Nonetheless, more recently it has been found that "homoenolate esters" actually exist if the appropriate metal, ZnCl2 for example, is used [16], which reacts with carbonyl derivatives in the presence of one equivalent of Me SiCl to give 1,4-D systems by means of a "homo-... 

Representations of those possibilities that have been exemplified are given in Table 10. The more synthetically useful processes are discussed in greater detail in Section 4.16.9 and reference is given to the relevant subsection in the table. (Note Cycloreversion of a 1,2,3-trioxolane to give a carbonyl oxide, which can undergo [3 + 2] reactions with carbonyl derivatives, is included in Section 4.16.8.)... 

The difluoromethylene ylides react with carbonyl derivatives (aldehyde, lactone) to afford gem-difluoromethylene compounds.They are generated starting from halogenodifluoromethane with triphenylphosphine (or trisaminophosphine) or starting from zinc and a phosphonium salt (or a phosphine oxide)." ° ... 

The direct synthesis of ureas from amines with carbonyl derivatives is not always convenient because of the pressure equipment that is necessary. On the industrial production scale this is usually no problem. 

SCHEME 91. Reaction of allenic, propargylic and allylic zinc reagents with carbonyl derivatives... 

In recent years there has been a growing interest in the use of carbonyl ylides as 1,3-dipoles for total synthesis.127-130 Their dipolar cycloaddition to alkenic, alkynic and hetero multiple bonded dipolaro-philes has been well documented.6 Methods for the generation of carbonyl ylides include the thermal and photochemical opening of oxiranes,131 the thermal fragmentation of certain heterocyclic structures such as A3-l,3,4-oxadiazolines (141) or l,3-dioxolan-4-ones132-134 (142) and the reaction of carbenes or car-benoids with carbonyl derivatives.133-138 Formation of a carbonyl ylide by attack of a rhodium carbenoid... 

The condensation of the 1-methyl group in 2-benzopyrylium salts 92 with carbonyl derivatives such as aromatic aldehydes (70KGS1308) in acetic acid gives rise to 1-styryl-substituted salts 94. The reaction proceeds similarly with orthoesters (74KGS37), isocoumarin derivatives, and di-methylformamide (DMF) (80KGS193) or azomethines (82KGS465). The... 

Aza-allyl anions also react with carbonyl derivatives to give iV-protected P-hydroxyamines and p-amino alcohols after reduction or hydrolysis.334... 

Among these reactions, the photochemical cycloadditions of C=C bom which can create up to four asymmetric carbons during the photochemical sti are particularly interesting, and numerous synthetic applications of this react have been reported. Advances in the understanding of the origin of asymmefa induction, during addition of alkenes with carbonyl derivatives, cyclic enom and aromatic compounds, will be discussed in detail. 

In the reaction of allylic organozinc reagents with carbonyl derivatives (e.g., diisobutyl ketone), isomerization of the branched product (XXX) occurs to the thermodynamically more stable linear product (XXXI) (333). The ratio of linear to branched alcohol increases with longer reaction time, and this was taken as evidence that the branched alco-... 

Since hydrazone anion chemistry is complementary to more conventional deprotonation-electrophilic substitutions effected with carbonyl derivatives such as ketones and aldehydes, and since hydrazone chemistry involves two additional synthetic operations, the use of hydrazones has to have some additional advantages. Compensating for the additional synthetic effort required to prepare and hydrolyze the... 

Condensing certain hydrazine derivatives with carbonyl derivatives may, further, lead to heterocycles containing the structural unit of N,iV-acetals (aminals) for instance, 1,2,3,4-tetrahydrophthalazine (13) and formaldehyde give 5,7,9,14,16,18-hexahydrodiphthalazino[2,3-a 2, 3 -d]-,s-tetrazine (14) 970... 

Nucleophilic strength for a given substituent can be measured in terms of the rate of the Sn2 reaction or in reactions with carbonyl derivatives. The relative rates of several nucleophiles were determined by reaction with iodomethane and are shown in Table 2.13. As mentioned previously, several factors contribute to nucleophilic strength. Electronic effects are important, as illustrated by the electron releasing methyl group, which should make methoxide more nucleophilic than hydroxide. The rate of the Sn2 reaction of sodium hydroxide with iodomethane is 1.3 x lO" M s whereas the rate with sodium methoxide with iodomethane is 2.51 x 1Q2 M- s-1.98... 

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