Aldehyde-alkenes => allylic

Using the above procedures, allyl a-azido alkyl ethers of type 281 were prepared by employing an unsaturated alcohol such as allyl alcohol [76] (Scheme 32). The reaction of an aldehyde with allyl alcohol and HN3 in a ratio of 1 3 9 carried out in the presence of TiCl4 as catalyst provided azido ethers 281, 283, and 285 in 70-90% yield. The ratio of reagents is critical to ensure a high yield of azido ether and to prevent formation of acetal and diazide side products [75]. Thermolysis of azido alkenes 281, 283, and 285 in benzene (the solvent of choice) for 6-20 h led to 2,5-dihydrooxazoles 282,284, and 286, respectively, in 66-90% yield. 

On the other hand, the pure (Z)-isomer of 1 on treatment with sec-butyllithium in THF generates the more susbstituted vinyllithium reagent 3. Thus by use of either sequence stereoselective routes are possible to alkenes, allylic aldbhols, and aldehydes. ... 

Alkenyllithiums generated from trisylhydrazones react with electrophiles such as primary alkyl bromides, aldehydes, ketones, dimethylformamide, CO2, chloro-trimethylsilane, or 1,2-dibromoethane to furnish substituted alkenes, allylic alcohols, a,(3-unsaturated aldehydes, a,P-unsaturated acids, alkenylsilanes, or alkenyl bromides, respectively, as exemplified below for the preparation of an allylic alcohol and an a,P-unsaturated aldehyde. ... 

As mentioned above, although some examples of intramolecular MBH reactions have been reported in the literature, this aspect is still in its infancy. Most known reports are based on the cyclizations of combinations of enone-enone, enone-acrylate, enone-aldehyde, unsaturated thioester-aldehyde, enone-allylic carbonate frameworks, etc. More recently, Krafft et al. have developed a novel, entirely organo-mediated intramolecular MBH reaction by using allyl chloride 277 as an alternative electrophile to afford densely functionalized cyclic enones 278. This reaction tolerates modification of the enone and the use of primary and secondary allylic chlorides and generates both five-and six-membered rings in excellent yields. Both mono- and disubstituted alkenes are formed with excellent selectivity in the absence of a transition metal catalyst (Scheme 1.100). ... 

The oxidation of higher alkenes in organic solvents proceeds under almost neutral conditions, and hence many functional groups such as ester or lac-tone[26,56-59], sulfonate[60], aldehyde[61-63], acetal[60], MOM ether[64], car-bobenzoxy[65], /-allylic alcohol[66], bromide[67,68], tertiary amine[69], and phenylselenide[70] can be tolerated. Partial hydrolysis of THP ether[71] and silyl ethers under certain conditions was reported. Alcohols are oxidized with Pd(II)[72-74] but the oxidation is slower than the oxidation of terminal alkenes and gives no problem when alcohols are used as solvents[75,76]. 

In contrast to oxidation in water, it has been found that 1-alkenes are directly oxidized with molecular oxygen in anhydrous, aprotic solvents, when a catalyst system of PdCl2(MeCN)2 and CuCl is used together with HMPA. In the absence of HMPA, no reaction takes place(100]. In the oxidation of 1-decene, the Oj uptake correlates with the amount of 2-decanone formed, and up to 0.5 mol of O2 is consumed for the production of 1 mol of the ketone. This result shows that both O atoms of molecular oxygen are incorporated into the product, and a bimetallic Pd(II) hydroperoxide coupled with a Cu salt is involved in oxidation of this type, and that the well known redox catalysis of PdXi and CuX is not always operalive[10 ]. The oxidation under anhydrous conditions is unique in terms of the regioselective formation of aldehyde 59 from X-allyl-A -methylbenzamide (58), whereas the use of aqueous DME results in the predominant formation of the methyl ketone 60. Similar results are obtained with allylic acetates and allylic carbonates[102]. The complete reversal of the regioselectivity in PdCli-catalyzed oxidation of alkenes is remarkable. 

When allylic alcohols are used as an alkene component in the reaction with aryl halides, elimination of /3-hydrogen takes place from the oxygen-bearing carbon, and aldehydes or ketones are obtained, rather than y-arylated allylic alcohoIs[87,88]. The reaction of allyl alcohol with bromobenzene affords dihydrocinnamaldehyde. The reaction of methallyl alcohol (96) with aryl halides is a good synthetic method for dihydro-2-methylcinnamaldehyde (97). 

Allylic carbonates are most reactive. Their carbonylation proceeds under mild conditions, namely at 50 C under 1-20 atm of CO. Facile exchange of CO2 with CO takes place[239]. The carbonylation of 2,7-octadienyl methyl carbonate (379) in MeOH affords the 3,8-nonadienoate 380 as expected, but carbonylation in AcOH produces the cyclized acid 381 and the bicyclic ketones 382 and 383 by the insertion of the internal alkene into Tr-allylpalladium before CO insertion[240] (see Section 2.11). The alkylidenesuccinate 385 is prepared in good yields by the carbonylation of the allylic carbonate 384 obtained by DABCO-mediated addition of aldehydes to acrylate. The E Z ratios are different depending on the substrates[241]. 

Mixtures of anhydrous hydrogen fluoride and tetrahydrofuran are successfully used as fluorinating agents to convert 1,1,2-trifluoro-l-allcen-3-ols, easily prepared from bromotrifluoroethene via lithiation followed by the reaction with aldehydes or ketones, to 1,1,1,2-tetrafluoro-2-alkenes The yields are optimal with a 5 1 ratio of hydrogen fluoride to tetrahydrofuran The fluorination reaction involves a fluonde lon-induced rearrangement (Sf,j2 mechanism) of allylic alcohols [65] (equation 40)... 

In a related reaction, pyrolysis of allylic ethers that contain at least one a hydrogen gives alkenes and aldehydes or ketones. The mechanism is also pericyclic"" ... 

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