A, -Unsaturated alkylation

A new approach to spirolactams involving the thermal reaction of A-unsaturated alkyl /1-carboxamidoenamines in which the enamine is the hetero-ene component has been reported.326 A-Alkylnitrilium salts have been shown to undergo ene reactions with electron-rich alkenes to afford either 2-azoniaallene salts (where the nitrilium salt acts... 

Ordinarily nucleophilic addition to the carbon-carbon double bond of an alkene is very rare It occurs with a p unsaturated carbonyl compounds because the carbanion that results IS an enolate which is more stable than a simple alkyl anion... 

A necessary feature of the alkylation reaction section is the use of two reactors the first-stage reactor completes the major part of the alkylation reaction, and in the second-stage reactor the last traces of unsaturated hydrocarbons react, and a sizable portion of the soluble polyaromatics is removed. Modem units with lower-diene-containing feeds employ a single alkylation reactor (79). 

A number of alternative multi-step procedures for the synthesis of a-tert-alkyl ketones are known, none of which possess wide generality. A previous synthesis of 2-tert-penty1cyclopentanone involved reaction of N-1-cyclopentenylpyrrol 1 dine with 3-chloro-3-methy1-l-butyne and reduction of the resulting acetylene (overall yield 46 ). However, all other enamines tested afford much lower yields. Cuprate addition to unsaturated ketones may be useful in certain cases. Other indirect methods have been briefly reviewed. ... 

The influence of alkyl substituents on the asynchronous transition-state structure of the BF3-catalyzed carbo-Diels-Alder reaction of a,/ -unsaturated aldehydes with 1,1-dimethyl-l,3-butadiene derivatives has been investigated by Dai et al. [13]. 

Removal of the unsaturated side-chain appendage from C-8 in 22 provides diol lactone 23 and allylic bromide 24 as potential precursors. In the synthetic direction, a diastereoselective alkylation of a hydroxyl-protected lactone enolate derived from 23 with allylic bromide 24 could accomplish the assembly of 22, an intermediate that possesses all of the carbon atoms of PGF2o- It was anticipated that preexisting asymmetry in the lactone enolate would induce the... 

Addition products are exclusively obtained from the addition of a-lithiatcd alkyl sulfones to a,/i-unsaturaled ketones5-6, in contrast, 1,4-adducts were obtained as a mixture of diastereomers from the reaction of these anions with a./l-unsaturated esters. The extent of the diastereoselection, however, was not reported6. 

An interesting new method for the conversion of [I, y-epoxy sulfones (82) to cyclo-alkenones (85) has been developed61. It includes the addition of alkyllithium to y-hydroxy-a,/ -unsaturated sulfones generated from 82 and the alkylation of sulfonyl carbanion thus formed. Oxidation of the resulting y-hydroxy sulfone to 84 followed by elimination of benzenesulfinic acid gives the desired product 85 in good yields (equation 72)61. 

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. 

The stereospecific base-cleavage of the trimethylsilyl group in 1,3-dithiane 1-oxides 499 enables to obtain the specifically deuteriated products 500 (equation 303), A nitro group in y-nitroalkyl sulphoxides 501 (obtained by the Michael addition of nitroalkanes to a, j8-unsaturated sulphoxides) is replaced by hydrogen by means of tributyltin hydride (equation 304). This reagent does not affect the sulphinyl function. The overall procedure provides an efficient method for the conjugate addition of alkyl groups to a, -unsaturated sulphoxides . ... 

Allylic sulfones, such as 242, isomerize to a, -unsaturated sulfones 243 upon treatment with a catalytic amount of potassium t-butoxide in dry THF. The a, -unsaturated sulfones can be converted to the corresponding olefins upon desulfonation with sodium amalgam or aluminium amalgamSince treatment of allylic sulfones with potassium-graphite gives 2-alkenes, alkylation of allylic sulfones and subsequent desulfonation is a useful process for the synthesis of olefins, as shown in Scheme 6. 

Dimetal derivatives 283 of alkyl and benzyl phenyl sulfones were found to react with aldehydes or ketones to give a,) -unsaturated phenyl sulfones 284 in good yields . 

The central bond of the l-(arylsulfonyl)bicyclo[1.1.0]butane system behaves like the double bond of a, ) -unsaturated sulfones to give alkyl-substituted cyclobutyl aryl sulfones on treatment with organometallic reagents (equation 20). This method has been applied... 

Several examples of conjugate addition of carbanions carried out under aprotic conditions are given in Scheme 2.24. The reactions are typically quenched by addition of a proton source to neutralize the enolate. It is also possible to trap the adduct by silylation or, as we will see in Section 2.6.2, to carry out a tandem alkylation. Lithium enolates preformed by reaction with LDA in THF react with enones to give 1,4-diketones (Entries 1 and 2). Entries 3 and 4 involve addition of ester enolates to enones. The reaction in Entry 3 gives the 1,2-addition product at —78°C but isomerizes to the 1,4-product at 25° C. Esters of 1,5-dicarboxylic acids are obtained by addition of ester enolates to a,(3-unsaturated esters (Entry 5). Entries 6 to 8 show cases of... 

---