Cycloaddition with enamines

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

Stable sulfenes have been isolated by treating methanesulfonyl chloride, with triethylamine or trimethylamine in acetonitrile solvent at -40°C (165,166). These stable sulfenes undergo 1,2 cycloaddition with enamines to form the expected thietanes (trimethylenesulfones). 

Nitrilimines can be produced by treating halogenated hydrazones with a base such as triethylamine. These nitrilimines undergo 1,3 cycloaddition with enamines to form pyrazoles (181-183). This is shown by the reaction of the pyrrolidine enamine of cyclohexanone with diphenyinitrilimine to... 

For more reactive electrophilic alkenes possessing two or more electron-withdrawing groups, cycloadditions with enamines occur under mild conditions. The cycloadditions of A,A -dimethyl-2-methylprop-1-enamine (12) with a series of electrophilic alkenes 13 proceed at temperatures ranging from — 30 °C to room temperature in short reaction times to give good to very good yields of the aminocyclobutanes 14.30... 

Phthalazines undergo [2 + 4] cycloaddition with enamines to give naphthalene derivatives. Pyrimidines also react as azadienes in reactions with enamines, e.g. (398 — 399). 

The readily available methyl 3,3-dimethylcyclopropene-l-carboxylate (III/54) undergoes [2+2] cycloaddition with enamines e.g. the morpholine derivative III/55 to give 2-aminobicyclo[2.1.0]pentane derivatives, e.g. III/56. These compounds are transformed into cyclopentane derivatives, e.g. methyl 4-hydroxy-2,5,5-trimethyl-1-cyclopentenecarboxylate (III/57) by treatment with dilute mineral acids. 

Diazadienes 370 and 371, formed in situ from the corresponding silyl imine and phenylisocyanate, readily undergo [4 + 2] cycloadditions with enamines derived from butyraldehyde and cyclohexanone leading, after deamination, to pyrimidone 372 and pyrimidothione 373, respectively224. 

Sulfonyl imides(RN=S02), generated from alkylsulfamoyl chloride (RNHSOjCl) and triethylamine, react with enamines in the same way as sulfenes do, to give four-membered heterocycloadducts such as 210 Phenyl isocyanate undergoes [2 -t- 2] cycloaddition with enamines affording azetidinones (211) whereas azetidinothiones (212) have been obtained from the reaction of isothiocyanates with enamines without j8-hydrogens . ... 

Acyl isothiocyanates have been shown to participate in [4 + 2] cycloadditions with enamines,98 imines," ketenimines,100 and hydrazones.101 Similar reports have detailed the [4 + 2] cycloadditions of thioacyl isothiocyanates with the carbon-carbon double bond of ketenes, ketenimines, and enamines as well as the carbon-nitrogen double bond of imines, carbodii-mides, and isocyanates.102... 

Cycloadditions. The same type of Fischer-type complexes undergo cycloaddition with enamines. Interestingly, acyclic and cyclic enamines afford products of different skeletons. 

X ]-antara,antara-Copc rearrangement Dimethyl acetylenedicarboxylate has been used in [2 + 2]cycloadditions with enamines to give cyclobutenes, which in turn have been used as intermediates in preparations of dihydrothiepins and benzo[h]oxepins. Stable bicyclic 1,2-dimethoxycarbonylcyclobutenes have also been obtained from dimethyl acetylenedicarboxylate with 1-alkyl-1,4-dihydropyridines and 1-alkyl-1,4-dihydroquinolines. The former products showed no tendency to isomerize whereas benzazocine derivatives could be obtained from the latter compounds simply by refluxing them in benzene. 

The earliest examples of this process involve thermal cycloadditions with enamines as the 2jt-components in which the cycfic nitronates could be isolated [65]. Subsequently, silyl enol ethers were shown to react with nitroalkenes in the presence of Lewis acids, such as TiCl2(0-i-Pr)2 [66f]. In this same smdy, Seebach showed that the nitronates... 

The strongly nucleophilic enamines are among the first reported dienophiles for nitroalkene cycloadditions [85]. Thus, nitroalkene 51 undergoes thermal [4 + 2] cycloaddition with enamine 52 to provide nitronate 53 (Scheme 16.11) [86]. 

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