Crotyl acetal

Durandetti et al. have described iron-catalyzed electrochemical allylation of carbonyl compounds with allylic acetates (Equation (27)).333 In the case of aldehydes, slow addition of the corresponding aldehyde is required in order to avoid pinacol formation. With crotyl acetate (R3 = Me), the reaction proved to be highly regioselective, providing almost exclusively branched homoallylic alcohols 150. 

Syntheses of primary ally lie amines have been reviewed183. The regiochemistry of the reaction of iron carbonyl complexes with nucleophiles such as morpholine has been investigated. The (r 3-crolyl) Fe+(CO)4 BF4- complexes 172 (R1 = H R2 = Me or R1 = Me R2 = H) undergo preferential attack at the less substituted allyl terminus to yield allylic amines 173. The (/j2-crotyl acetate) Fe(CO)4 complex 174, on the other hand, does not react with morpholine184. 

When dendritic catalyst 2 was applied in the allylie amination of crotyl acetate and piperidine in the CFMR, a similar rapid deaetivation of the eatalyst was observed. 

Fig. 5. Application of dendrimeric ligand 4 in the allylic amination of crotyl acetate and piperidine using a CFMR (% conversion of crotyl acetate in the product stream vs substrate flow), (a) P/Pd = 2, (b) P/Pd = 4, Koch MPF-60 NF membrane, molecular weight cut-off = 400 Da) )18b).

The supramolecular guest—Pd—dendrimer complex was found to have a retention of 99.4% in a CFMR and was investigated as a catalyst for the allylic ami-nation reaction. A solution of crotyl acetate and piperidine in dichloromethane was pumped through the reactor. The conversion reached its maximum ca. 80%) after approximately 1.5 h (which is equivalent to 2—3 reactor volumes of substrate solution pumped through the reactor). The conversion remained fairly constant during the course of the experiment (Fig. 8). A small decrease in conversion was observed, which was attributed to the slow deactivation of the catalyst. This experiment, however, clearly demonstrated that the non-covalently functionalized dendrimers are suitable as soluble and recyclable supports for catalysts. 

In another variation, the intermediate aldol product 64, with an extra hydroxy group in the y-position, was used to construct the furan ring of rosefuran (65), a trace component of rose oil (Scheme 6.56) (285). Here, the reaction of the nitropentene derivative 61 with crotyl acetate (62) afforded the 3,4,5-trisubstituted isoxazoline (63) in moderate yield. Removal of the acetyl group by saponification of the cycloadduct, subsequent demasking of the aldol moiety using Mo(CO)6, and exposure of the ketodiol (64) to acid gave the target compound 65 (285). 

There have been no significant advances in the area of platinum-catalyzed allylic alkylations since the first work in 1985 [208], With the platinum complex derived from DIOP, low ee (11%) and modest regioselectivity (4 1) were obtained for the alkylation of (E)-crotyl acetate with dimethyl malonate. 

The resulting peripheral phosphine-functionalized dendrimers were used as a ligand in the palladium-catalyzed allylic amination of crotyl acetate in a CFMR. The active catalysts were prepared by mixing all three components the dendrimer, the phosphine ligand and a suitable palladium precursor [(crotyl)PdCl]2. The catalytic activity and selectivity of 16 in a batch process... 

Pd-catalyzed allylic amination of crotyl acetate by piperidine, while exhibiting a reduced rate as is commonly observed for heterogenized systems (90% conversion achieved after 30 min compared with 5 min for the homogeneous system). Interestingly, the catalyst could be recycled three times via a simple filtration step. Subsequently, the catalyst was separated from the support and the support was uploaded with hydroformylation catalysts. 

Table 7 Results of the Pd-catalyzed allylic amination of crotyl acetate and piperidine, comparing the supramolecular dendrimeric catalyst with the corresponding monomer3...

Negishi [87] found that phenylmagnesium bromide reacted with ( )-crotyl acetate in the presence of Pd(PPh3)4 to afford a nearly 1 1 mixture ofSN2and Sn2 products [Eq. (86)]. 

Numerous monographs [4] and reviews [5] on the famous Wittig reaction have been written since its discovery in 1953. The BASF vitamin-A synthesis depends in the final step on a Wittig coupling between vinyl-)ff-ionol (C15) and y-formyl-crotyl acetate (C5). This application was developed by Pommer et al. [6] of BASF in the 1960s. 

The efficiency of the dendrimer-supported palladium complex was studied using the addition of crotyl acetate to piperidine (Scheme 26). The reaction was found to proceed with essentially the same conversion (72%) and the product distribution of linear trans (33%), linear cis (6%), and branched (61%) products as observed for the same loading of the monomeric catalyst. 

Scheme 26 Amination of crotyl acetate catalyzed by a dendrimer-supported phosphine catalyst. ...

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