Unsaturated aldehydes rearrangement

The 5-oxohexanal 27 is prepared by the following three-step procedure (1) 1,2-addition of allylmagnesium bromide to an a, / -unsaturated aldehyde to give the 3-hydroxy-1,5-diene 25, (2) oxy-Cope rearrangement of 25 to give 26, and (3) palladium catalyzed oxidation to afford 27. The method was applied to the synthesis of A -2-octalone (28), which is difficult to prepare by the Robinson annulation[25]. 

The Pd(0)-catalyzed rearrangement of the iV-allylenamine 800 in CF3CO2H affords the (5, -unsaturated imine 801, which is hydrolyzed to give the 7, 8-unsaturated aldehyde 802[498]. The vinyloxaspirohexane 803 undergoes rearrangement-ring expansion to give the cyclopentanone 804 in the presence of 1 equiv. of p-nitrophenol[499]. 

Ethynyl carbinols rearrange to conjugated unsaturated aldehydes. Copper or silver salts cataly2e isomeri2ation of the acetate to an aHenic acetate, which can be hydroly2ed to an unsaturated aldehyde (204). 

CLAISEN - IRELAND Rearrangment Rearrangement ol allyl phenyl ethers to o (or p-)allylphenols or of allyl vinyl ethers to y.S-unsaturated aldehydes or ketones (Claisen) Rearrangement ol allyl esters as enolale anions to y.S-unsaturated acids (Ireland)... 

In the presence of catalytic amounts of Pd(0), silicon-substituted vinyloxiranes can rearrange into the corresponding ot-silyl- 3,y-unsaturated aldehydes (Scheme 9.34) [151]. Treatment of 80 with Pd(OAc)2 and P(OPh)3 results in the formation of 7t-allylpalladium complex 81. Bond rotation to give 82, followed by migration of the silyl moiety, affords aldehyde 83, which is trapped in situ to provide the Felkin-Anh product 84. The reaction proceeds with retention of configuration and the ee of the starting material is retained in the product. The size of the silicon substituents is critical for the outcome of the reaction, as is the choice of ligands on palladium. 

When X=OH, this conversion of acetylenic alcohols to unsaturated aldehydes or ketones is called the Meyer-Schuster rearrangement The propargyl rearrangement can also go the other way that is, 1-haloalkenes, treated with organocopper compounds, give alkynes. ... 

Reaction of the carbanion of chloromethyl phenyl sulphoxide 409 with carbonyl compounds yields the corresponding 0-hydroxy adducts 410 in 68-79% yield. Each of these compounds appears to be a single isomer (equation 242). Treatment of adducts 410 with dilute potassium hydroxide in methanol at room temperature gives the epoxy sulphoxides 411 (equation 243). The ease of this intramolecular displacement of chloride ion contrasts with a great difficulty in displacing chloride ion from chloromethyl phenyl sulphoxide by external nucleophiles . When chloromethyl methyl sulphoxide 412 is reacted with unsymmetrical ketones in the presence of potassium tcrt-butoxide in tert-butanol oxiranes are directly formed as a mixture of diastereoisomers (equation 244). a-Sulphinyl epoxides 413 rearrange to a-sulphinyl aldehydes 414 or ketones, which can be transformed by elimination of sulphenic acid into a, 8-unsaturated aldehydes or ketones (equation 245). The lithium salts (410a) of a-chloro-/ -hydroxyalkyl... 

Dihydro-2H-pyran-2-ones (e. g., 4-195) are valuable intermediates in the synthesis of several natural products [67]. Hattori, Miyano and coworkers [68] have recently shown that these compounds can be easily obtained in high yield by a Pd2+-catalyzed [2+2] cycloaddition of ct, 3-unsaturated aldehydes 4-192 with ketene 4-193, followed by an allylic rearrangement of the intermediate 4-194 (Scheme 4.42). In this reaction the Pd2+-compound acts as a mild Lewis acid. a,(3-unsaturated ketones can also be used, but the yields are below 20%. 

The Claisen rearrangement is an electrocyclic reaction which converts an allyl vinyl ether into a y,8-unsaturated aldehyde or ketone, via a (3.3) sigmatropic shift. The rate of this reaction can be largely increased in polar solvents. Several works have addressed the study of the reaction mechanism and the electronic structure of the transition state (TS) by examining substituent and solvent effects on the rate of this reaction. 

The reaction was achieved through transfer vinylation of 67 with 68 by action of the [IrCl(cod)]2 complex to afford allyl homoallyl ethers 69, followed by a Claisen rearrangement of the ether 70. The Claisen rearrangement of allyl homoallyl ethers to y,5-unsaturated aldehydes has been reported previously [6]. 

Acid-catalyzed rearrangement of tertiary a-acetylenic (terminal) alcohols, leading to the formation of a,(3-unsaturated ketones rather than the corresponding a,(3-unsaturated aldehydes. Cf. Meyer-Schuster rearrangement. 

In order to determine whether the partial suppression of the free-rotor effect was required for the success of the ODPM rearrangement process, the study was extended to the aldehyde 33 [51], When 33 is irradiated (15 min), under similar conditions to those used for 29, the cyclopropyl aldehyde 34, resulting from an ODPM rearrangement, was obtained, as the tran -diastereoisomer, in 90% isolated yield. This result demonstrated clearly that the ODPM reactivity of (3,y-unsaturated aldehydes is not restricted to cyclic compounds, such as 29, but can also be extended to acyclic derivatives. Therefore, the suppression of the free-rotor effect is not essential for the success of the rearrangement and the reaction is probably controlled by both the excitation of the molecule to the TiCtt, -it )... 

These unexpected results suggest a modification of the conclusions reached in our earlier studies. Specifically, the observations indicate that in order to detect ODPM photoreactivity in p,7-unsaturated aldehydes, substiments should be present to stabilize intermediate biradicals in the rearrangement pathway, but they should not enhance alternative reactions, such as allylic homolytic cleavage. Further studies will be necessary to confirm this hypothesis and to determine the scope of these new reactions. 

Another intriguing observation made in our preliminary studies in this area is that p,7-unsaturated aldehyde 23 undergoes photoinduced ODPM rearrange-... 

In an attempt to establish the limits for ODPM reactivity of (B.y-unsaturated aldehydes, we have extended our studies to a series of aldehydes 65, (Scheme 10) which are monosubstituted at C-2. Triplet-sensitized irradiation of 65 leads to the formation of the corresponding cyclopropanecarbaldehydes 66 [59] (Scheme 10). The diphenyl-substituted aldehydes 65b and 65d yield, in addition to the ODPM products, the corresponding alkenes 67a and 67b, resulting from photodecarbonylation. The formation of these alkenes is probably due to stabilization of the radical, formed by allylic cleavage, by diphenyl conjugation. The ODPM rearrangement of aldehydes 65 is diastereoselective, yielding only one diastereoisomer of 66 (Scheme 10). 

From the foregoing discussion, it is clear that DPM rearrangements are very general for a variety of 1,4-unsaturated systems, such as, 1,4-dienes, (3,7-unsaturated aldehydes and ketones, and different 1-aza-1,4-diene derivatives. Surprisingly, the literature was devoid of studies describing the photoreactivity of the closely related 2-aza-1,4-diene derivatives. For many years, the only studies in this area were carried out by Mariano and his co-workers [60] on the photochemistry of iminium salts derived from 2-aza-1,4-dienes. The results obtained demonstrated the synthetic utility of the photocyclizations of iminium salts to different heterocycles, in reactions that are initiated by intramolecular single electron transfer [60]. 

The study has been extended to azadienes 82-85. The snbstitntion patterns present in these compounds has proved to be adequate to promote the ODPM rearrangement in [3,7-unsaturated aldehydes [4] and the 1-ADPM reaction in 1-aza-1, 4-dienes [4]. However, triplet-sensitized irradiation of compounds 82-85 yields complex mixtures of products that have not been identified. These results show that a clear difference exists between the DPM reactivity of 2-aza-1,4-dienes and the other DPM processes previously reported [65]. The differences are difficult to explain and further studies are underway to clarify this point. 

---