Pivaldehyde

Methylene, 287 Pivaldehyde Acetal, 289 Acetonide, 289 Cyclohexylidene. 289 Diphenylmethylene, 289 Ethyl Orthoformate, 290 Diisopropylsilylene Derivative, 290... 

The acetal is prepared from a catechol and pivaldehyde with TMSCl catalysis. ... 

From a hydroxy acid pivaldehyde, acid catalyst. ... 

Reaction of aldehydes and ketones with methanol or glycols at ambient temperature in the presence of excess trimethylchlorosilane (TCS) 14 to form acetals, hexamethyldisiloxane 7, and HCl is achieved very simply [28]. Thus cyclohexanone and diacetyl react with free glycol and TCS 14 to give the acetals 392 and 405 in 95% yield [28]. Reaction of phenylglyoxal with methanol in the presence of trimethylchlorosilane 14 affords the acetal 406 in 83% yield [28], whereas catechol 79 is converted by pivaldehyde into acetal 407 in 91% yield [29] (Scheme 5.5). 

Reaction of ketones such as 1-menthone 398 with silylated glycolic acid 417 in the presence of catalytic amounts of TMSOTf 20 provides an lil-mixture of the l,3-dioxolan-4-ones 418 and 419 [35, 36]. Likewise, other aldehydes and ketones [37, 38] and pivaldehyde [39] react with substituted silylated glycohc adds 420 a, b and yS-hydroxy acids 420c to give, e.g., 421 a, b and 421c as mixtures [37-40]. Reaction of pivaldehyde with the persilylated hydroxy acid 420 d and TMSOTf 20 to... 

Redistilled N, O-persilylated L-proline 438 reacts with pivaldehyde in pentane at ambient temperature to give the 0,N-acetal 439 in 78% yield in the presence of LDA this condenses, a to the carbonyl group, with N-alkyl-2-pyrrole aldehydes [48] (Scheme 5.14). 

With unhindered aldehydes such as cyclohexanecarboxaldehyde, the diastereoselec-tivity is higher than 95%, with the F-boronate giving the anti adduct and the Z-boronate giving the syn adduct. Enantioselectivity is about 90% for the F-boronate and 80% for the Z-boronate. With more hindered aldehydes, such as pivaldehyde, the diastere-oselectivity is maintained but the enantioselectivity drops somewhat. These reagents also give excellent double stereodifferentiation when used with chiral aldehydes. For example, the aldehydes 3 and 4 give at least 90% enantioselection with both the E- and Z-boronates.43... 

Pipecolines, m3 81 thru m3 83 1-Piperazinoethanol, hi29 1-Piperidinecarboxyaldehyde, f40 Piperonal, m250 Piperonyl butoxide, m252 cv.v-Piperylene, pi6 Pivaldehyde, d677... 

Starting from 2,4,6-octatriene and pivaldehyde, the conjugated homoallylic alcohol 8 is obtained as the sole product. Cycloheptatriene-derived complexes react with aldehydes and C02 to afford mixtures of the isomeric 1,3- and 1,4-cycloheptadienyl carbinols or acids, respectively. Interestingly, analogous reactions with methyl chloroformate or dimethyl carbamoyl chloride produce the conjugated dienyl ester 9 or amide 10 as unique products [19,20]. 

Bouveault reactionDMF is recommended for formylation of tertiary Grig-nard reagents. Thus pivaldehyde can be obtained in 57-61% yield by reaction of r-butylmagnesium chloride with twofold excess of DMF in ether. 

Catalyst 329, prepared from trimethylaluminum and 3,3/-bis(triphenylsily 1)-1,1 /-bi-2-naphthol, allowed the preparation of the endo cycloadduct (2S )-327 with 67% ee. The use of non-polar solvents raised the ee, but lowered the chemical yield213. Recently, it was reported that the reaction to form 327 exhibited autoinduction when mediated by catalyst 326214. This was attributed to a co-operative interaction of the cycloadduct with the catalyst, generating a more selective catalytic species. A wide variety of carbonyl ligands were tested for their co-operative effect on enantioselectivity. Sterically crowded aldehydes such as pivaldehyde provided the best results. Surprisingly, 1,3-dicarbonyl compounds were even more effective than monocarbonyl compounds. The asymmetric induction increased from 82 to 92% ee when di(l-adamantyl)-2,2-dimethylmalonate was added while at the same time the reaction temperature was allowed to increase by 80 °C, from -80 °C to 0°C. 

Fluoride ion promoted cleavage of propynylsilanes and subsequent reaction of the carbanion with carbonyl compounds produces allenic compounds. The reaction with formaldehyde and pivaldehyde fails, but both the allenic and acetylenic products are obtained from the reaction with acrolein and benzaldehyde [49]. Allylsilanes react with carbonyl compounds to produce but-3-en-l-ols [50],... 

Two hindered phosphoranylidenephosphines, ArP=PMc3 [76 Ar = 2,6-dimesityl-phenyl and 2,4,6-tri(r-butyl)phenyl], have been prepared and are stable in the absence of air and water. As the resonance suggests, they can enter into phospha-Wittig reactions to produce phosphaalkenes (77). The reaction gave high yields of ( )-(77) in a few hours for a range of benzaldehydes (p-Cl/N02/0Me/NMe2/H, F5), and also for ferrocenecarboxaldehyde and pivaldehyde, but was unsuccessful for ketones. 

This is clearly illustrated in the example given below for the reaction of the methoxymethyl cation with pivaldehyde. There are four possible reaction channels for the unimolecular dissociation of the initially formed adduct, which is presumed to be of the form of a covalent species resulting from the interaction of the carbocation center of the methoxymethyl cation with the carbonyl oxygen of the aldehyde, 2. For smaller carbonyl compounds this adduct has been demon-... 

Figure 16. Metastable ion cyclotron resonance (MICR) spectra for the unimolecular dissociation of the chemically activated adduct ion derived from association of the methoxymethyl cation with pivaldehyde during a 2-s reaction delay at a pressure of pivaldehyde of 1.0 x 10 torr. The three spectra correspond to values of rf amplitude appropriate to eject transient intermediates with lifetimes longer than (a) 60 ps, (b) 80 ps, and (c) 1 70 ps. A partial pressure of CH4 of 1.0 x 10 torr was also present to thermalize ions. The peak at m/z 125 is a secondary reaction product of m/z 85.

Figure 17, Qualitative potential energy surface for the reaction of methoxymethyl cation with pivaldehyde. Energies in parentheses have units of kcal mol". ...

In connection with the enantioselective alkylation of Pro or 4-hydroxy-proline, the azabicyclo[3.3.0]octane system 81 was obtained after reaction with pivaldehyde (81HCA2704 85HCA155). In a more complex transformation A-protected L-Pro was transformed into the same bicyclic system (Scheme 49) (81JA1851 84JA4192). The product was prepared as a model substance in the total synthesis of pumiliotoxin. A related compound 82 was prepared from 5-(hydroxymethyl)-2-pyrrolidinone (prepared from L-pyroglutamic acid) by an acid-catalyzed condensation with benzaldehyde (86JOC3140). 

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