Reaction with aldehydes and ketones

Sodium borohydride, reaction with ketones and aldehydes,... 

Secondary phosphines with a /3-hydroxyethyl substituent, obtained by addition of primary phosphines to a-oxides, easily undergo a reaction with ketones and aldehydes, giving 1,3-oxaphospholanes (6) [Eq. (4)] (72T2587). 

Scheme 14 Equilibria in aldol reactions with ketone and aldehyde acceptors...

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. 

The other major synthetic use of alkyne anions is their reaction with ketones and aldehydes to give an alkynyl alcohol via nucleophilic acyl addition. The lithium salt of 1-propyne, for example, reacted with aldehyde 40 to give alcohol 41 as part of Smith s synthesis of (+)-acutiphycin.50 The reaction is selective for ketones and aldehydes in the presence of acid derivatives, if the acetylide is not present in large excess. l... 

Other titanium-based olefination reagents have been developed. Eisch used a zinc analog of the Tebbe reagent (688) in a reaction with benzophenone to give 1,1-diphenylethene in 78% yield. Similarly, Clawson et al. used 689 in olefination reactions with ketones and aldehydes. Alkoxytitanium reagents such as 690 have been employed, as in the conversion of cyclohexane carboxaldehyde to 1-cyclohexyl-1,3-butadiene (691), in 86% yield.In this olefination reaction, the (Z)-isomer predominated over the ( ) (96 4 Z/E). 

Other organometallic reagents have been reported to give Wittig-type olefination reactions with ketones and aldehydes. Typical examples are 700, 86 701,587 702,588 703,589 and 704.590 -phis list is certainly not exhaustive and is probably not completely representative. It does, however, illustrate some of the reagent types that have appeared and continue to appear. 

Bases lb. Id, and 9b catalyze the nitroaldol reaction with ketones and aldehydes at room temperature in the presence of MgS04 in generally superior yields [Eq. (14)] [123]. Moreover, ketone self-condensation was not problematic under our conditions. In a comparison of the effectiveness of Id with le and If in these reactions, le and If were more efficacious [71]. 

Because of this resemblance in reaction pattern, the term generalized aldol condensation has been applied to a broader group of reactions in which enolates or enols act as nucleophilic species in reactions with ketones and aldehydes. In general, the reactions in the addition phase of both base-catalyzed and acid-catalyzed aldol condensations are easily reversible. 

Trimethylsulfonium iodide undergoes ylid formation by reaction with 50% aqueous sodium hydroxide in the presence of catalytic tetrabutylammonium iodide [16]. The ylid thus formed reacts with aldehydes and ketones to form the corresponding epoxides (Eq. 14.7). The yields with aldehydes are considerably better than those with ketones. The fact that the reaction is slow (48 hours) may be due to the iodide of the catalyst. On the other hand, lauryldimethylsulfonium chloride undergoes reaction with ketones and aldehydes to yield epoxides under alkaline phase transfer conditions considerably more rapidly (6—10 hours). The enhanced rate of this methylene transfer reaction is probably due to the greater organic solubility of the lauryldimethylsulfonium cation [17]. Catalyst poisoning is observed with lauryldimethylsulfonium iodide. Similar reactions have been conducted under ion pair extraction conditions [18]. 

The Petasis reagent (Me2TiCp2, dimethyltitanocene) undergoes similar olefi-nation reactions with ketones and aldehydes. The originally proposed mechanism [3] was very different from that of Tebbe olefmation. However, later experimental data seem to suggest that both Petasis and Tebbe olefmation share the same mechanism, i.e. the carbene mechanism involving a four-membered titanium oxide ring intermediate [6]. 

The Petasis reagent (Me2TiCp2, dimethyltitanocene) undergoes similar olefination reactions with ketones and aldehydes [5]. However, the mechanism is very different. 

A combination of iodomethyltrimethylsilane and Sm(OTf)2 also works as a methylenating reagent for carbonyl compounds (Scheme 2.28). When this reagent is applied to the reaction with ketones and aldehydes in THF/HMPA at room temperature, the carbonyl compounds are smoothly methylenated this process is known as the samarium-Peterson reaction [69]. 

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