Reactions crotylation

The six-member ed transition state for the reaction of an allylic borane or boron ate is very reminiscent of the cyclic transition state for the aldol reaction you met in Chapter 34. In this case the only change is to replace the oxygen of the enolate with a carbon to make the allyl nucleophile. The transition state for the aldol reaction was a chair and the reaction was stereospecific so that the geometry of the enolate determined the stereochemistry of the product aldol. The same is true in these reactions. -Crotyl boranes (or boronates) give anti homoallylic alcohols and Z-crotyl boranes (or boronates)... 

Some alcohols that have been converted into the corresponding fluorides by reactions with diethyldminosulfur trifluoride include 1-octanol, 2-methyl-2-butanol, isobutyl alcohol, cyclooctanol, ethylene glycol, crotyl alcohol, 2-phenylethanol, 2-bromoethanol, ethyl lactate, and ethyl a-hydrox3maphthaleneacetate. ... 

Allyiic rearrangements are observed m the reactions of allylic alcohols with dialkylaminosulfur trifluorides [95 130] Both crotyl alcohol and buten 3 ol give... 

Reaction of 2-(A -alkyl-A -benzylamino)- and 2-[A -(rraM-crotyl)-A -ben-zylamino]-3-formyl-4/7-pyrido[l,2-n]pyrimidin-4-ones (260, R = H, Me) with tosylamine gave compounds 268 via compounds 266 and 267 (96T13097). The results of kinetic studies and MP3 calculations on the 3-formyl derivatives 252, 260 and the imines 262, 263 suggested a concerted nature for azepine-ring formation. 

Reaction of 2-[A -(rra -crotyl)-A -benzylamino]-3-formyl-4/f-pyrido[l,2-n]pyrimidin-4-one (269) with chiral primary amines 270 and 271 gave mixtures of diastereoisomers of tetracyclic compounds 273 and tricyclic 275 (96T131]]). The chiral centers in 272 and 274 did not provide any stereocontrol for the formation of diastereomers 273 and 275, respectively. 

The reaction of crotyl organometallic compounds 1 with aldimines 2 results in linear 3 or branched 4 homoallylamines. 

To a solution of 0.18 g (1 mmol) of /V-benzylideneaniline in F.t,0 is added 0.194 g (1.1 mmol) of 9-(2-butenyl)-9-borabicyclo[3.3.1]nonane (crotyl-9-BBN) at — 78 °C. The reaction is quenched at O C with several drops of coned [ICl. The mixture is stirred overnight at r.t.. and a 3 N aq soln of NaOH is added at 0°C to make the solution basic. The mixture is extracted twice with ht20. dried, condensed, and filtered through a short column of silica gel (hexane/Et20 10 1) to remove the 9-BBN residue. 

As an example of the system in which parallel and consecutive reactions occur simultaneously, we have chosen the hydrogenation of crotonaldehyde, which may lead through two two-stage paths (via butyraldehyde and via crotyl alcohol) to the same final product, butanol... 

Fig. 9. Dependence of relative molar concentrations Wj/nA0 of reaction components on reciprocal space velocity W/F (hr kg mole 1) in the parallel-consecutive hydrogenation of crotonaldehyde. Temperature 160°C, catalyst Pt-Fe/Si02 (1% wt. Pt, 0.7% Fe), initial molar ratio of reactants G = 10. The curves were calculated (1—crotonaldehyde, 2—butyraldehyde, 3—crotyl alcohol, 4—butanol) the points are experimental values.

From the results of this kinetic study and from the values of the adsorption coefficients listed in Table IX, it can be judged that both reactions of crotonaldehyde as well as the reaction of butyraldehyde proceed on identical sites of the catalytic surface. The hydrogenation of crotyl alcohol and its isomerization, which follow different kinetics, most likely proceed on other sites of the surface. From the form of the integral experimental dependences in Fig. 9 it may be assumed, for similar reasons as in the hy-drodemethylation of xylenes (p. 31) or in the hydrogenation of phenol, that the adsorption or desorption of the reaction components are most likely faster processes than surface reactions. 

It is noteworthy that even a separate treatment of the initial data on branched reactions (1) and (2) (hydrogenation of crotonaldehyde to butyr-aldehyde and to crotyl alcohol) results in practically the same values of the adsorption coefficient of crotonaldehyde (17 and 19 atm-1)- This indicates that the adsorbed form of crotonaldehyde is the same in both reactions. From the kinetic viewpoint it means that the ratio of the initial rates of both branched reactions of crotonaldehyde is constant, as follows from Eq. (31) simplified for the initial rate, and that the selectivity of the formation of butyraldehyde and crotyl alcohol is therefore independent of the initial partial pressure of crotonaldehyde. This may be the consequence of a very similar chemical nature of both reaction branches. 

From the study of the influencing of single reactions by products and by other added substances and from the analysis of mutual influencing of reactions in coupled systems, the following conclusions can be drawn concerning adsorption of the reaction components. (1) With the exception of crotyl alcohol on the platinum-iron-silica gel catalyst, all the substances present in the coupled system, i.e. reactants, intermediate products, and final products, always adsorbed on the same sites of the catalytic surface (competitive adsorption). This nonspecificity was established also in our other studies (see Section IV.F.2) and was stated also by, for example, Smith and Prater (32), (2) The adsorption of starting reactants and the desorption of the intermediate and final products appeared in our studies always as faster, relative to the rate of chemical transformations of adsorbed substances on the surface of the catalyst. 

These authors48 have also examined the thermal stability of allylic arenesulfinates. They found that allyl, crotyl and a-methylallyl benzenesulfinates on heating underwent rearrangement to sulfones in low yields, but were unable to reach a decision with regard to reaction mechanism, mainly because the last two esters gave the same product crotyl phenyl sulfone. 

Some ten years later, Darwish and Braverman50,51 undertook a more extensive study of this rearrangement, which has revealed some unique features. These investigators examined the behavior of six different esters, namely allyl, crotyl, a-methylallyl, racemic and optically active a, y-dimethylallyl, cinnamyl and a-phenylallyl 2,6-dimethylbenzene-sulfinates under various reaction conditions. 

Between these two extremes of spontaneous rearrangement and total failure to rearrange, Braverman and Stabinsky36-38 have observed intermediate behavior. The reaction of crotyl alcohol with C13CSC1 afforded an equilibrium mixture of both crotyl trichlormethanesulfenate (13) and a-methylallyl trichloromethyl sulfoxide (14, equation 9). 

Addition of crotyl metal reagents to 4-acetoxy-l,3-dioxanes was utilized in the synthesis of dipropionate synthons [52] (Scheme 22). These reactions... 

It was suggested that this change in product distribution was due to the existence of an equilibrium between two types of complex, viz., a cr-butenyl-pentacyanocobaltate(III) and a 7r-butenyltetracyanocobaltate(III) 107, 109). However, further study of the kinetics and product distribution suggested the presence of two o-bonded complexes, viz., cr-but-l-en-3-yl and a-but-2-en-l-yl 24a). Direct evidence for the existence of a cyanide-dependent equilibrium between the a- and rr-bonded organocyanide complexes has been obtained from NMR studies of the complex prepared by the reaction of allyl halides with Co—H 109) (see also Section V,C). Both butadiene and crotyl chloride react with Co—H to give the same... 

Years earlier, Nicholas and Ladoulis had found another example of reactions catalyzed by Fe2(CO)9 127. They had shown that Fe2(CO)9 127 can be used as a catalyst for allylic alkylation of allylic acetates 129 by various malonate nucleophiles [109]. Although the regioselectivites were only moderately temperature-, solvent-, and substrate-dependent, further investigations concerned with the reaction mechanism and the catalytic species were undertaken [110]. Comparing stoichiometric reactions of cationic (ri -allyl)Fe(CO)4 and neutral (rj -crotyl ace-tate)Fe(CO)4 with different types of sodium malonates and the results of the Fe2(CO)9 127-catalyzed allylation they could show that these complexes are likely no reaction intermediates, because regioselectivites between stoichiometric and catalytic reactions differed. Examining the interaction of sodium dimethylmalonate 75 and Fe2(CO)9 127 they found some evidence for the involvement of a coordinated malonate species in the catalytic reactions. With an excess of malonate they... 

It was also shown that a cahonic allylnickel complex [(q3-crotyl)Ni P(OEt)3 2]PF6 catalyzes this reaction without added acid and that ds- and trans-1,3-pentadienes react with morpholine to give a mixture of 1,2- and 1,4-addition products [178]. 

In the synthesis shown in Scheme 13.15, racemates of both erythro- and threo-juvabione were synthesized by parallel routes. The isomeric intermediates were obtained in greater than 10 1 selectivity by choice of the E- or Z-silanes used for conjugate addition to cyclohexenone (Michael-Mukaiyama reaction). Further optimization of the stereoselectivity was achieved by the choice of the silyl substituents. The observed stereoselectivity is consistent with synclinal TSs for the addition of the crotyl silane reagents. 

Reisse used activated zinc for aqueous Barbier-type reactions.66 Submicromic zinc powder produced by pulsed sono-electroreduction is about three times more effective than the commercial variety. The stereochemical course of the allylation and propargylation of several aldehydes with crotyl and propenyl halides using zinc powder as the... 

The allylation of carbonyl compounds in aqueous media with SnCl2 can also employ allylic alcohols (Eq. 8.39)84 or carboxylates85 in the presence of a palladium catalyst. The diastereoselectivity of the reactions with substituted crotyl alcohols was solvent dependent. Improved diastereoselectivity was obtained when a mixture of water and THF or DMSO was used, instead of the organic solvent alone. 

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