Bis 4- methoxyphenyl -1,3,2,4-dithiadiphosphetane 2,4-Disulfide

Based on the empirical results/ X-ray-diffraction data/ and solution-phase NMR experiments/ a transition state model (6) has been advanced to explain the observed enantioselectivity. The presence of an ortho substituent in the A arylmaleimide reactant directs aluminum coordination to occur with the lone pair of electrons anti to the nitrogen atom. A 3,5-dimethylphenyl moiety present on the ethylenediamine framework blocks one face of the dienophile, resulting in approach of the diene from the backside. A considerable amount of spectroscopic evidence, most notably that obtained fromNOE (nuclear Overhauser effect) experiments, has been accumulated to support this model. A -arylmaleimide derivatives that lack an ortho substituent and other dienophiles (e.g., maleic anhydride) can coordinate to the aluminum catalyst in alternative modes such that the reactive olefin is far removed from the chiral environment of the ligand scaffold, thereby resulting in cycloaddition reactions that exhibit little or no enantioselectivity. 

The catalyst (1) has been used in the total asymmetric synthesis of marine natural products gracilin B and gracilin C. Treatment of 2-(trimethylsilyl)methylbutadiene with maleimide (4) (R = f-butyl) in the presence of 20 mol % (5 ,5)-(l) gave the cycloadduct (7) in 95% ee. This material was then converted to the targeted natural products in several steps (eq 2). 

Related Reagents. [A(V /-[l,2-Diphenyl-l,2-ethanediyl]-bis(l,l,l-trifluoromethanesulfonamidato)]methyl Aluminum. 

Solubility modestly sol boiling organic solvents such as toluene, chlorobenzene, anisole, dimethoxyethane. 

Form Supplied in yellowish evil-smelling crystals typical impurity is P4S10. 

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Bis-(4-methoxyphenyl)-[ 1,3,2,4]dithiadiphosphetane 2,4-disulfide, transforms the carbonyl groups of ketones, amides and esters into the corresponding thiocarbonyl compounds. 

Related Reagents. 1,3,2,4-Dithiadiphosphetane, 2,4-Bis-(methylthio)-2,4-disulfide (Davy-reagent methyl) 1,3,2, 4-dithiadiphosphetane, 2,4-Bis(ethylthio)-2,4-disulfide (Davy-reagent ethyl) 1,3,2,4-Dithiadiphosphetane, 2,4-Bis(phenyl-thio)-2,4-disulfide 1,3,2,4-Dithiadiphosphetane, 2,4-Bis-[(4-methox3q)henyl)thio]-2,4-disulfide 1,3,2,4-Dithiadiphosphetane, 2,4-bis(4-methoxyphenyl)-2,4-disulfide (Lawesson Reagent). 

Scheme 9.150. A representation of the use of Lawesson s reagent [2,4-bis(4-methoxyphenyl)-1,2,3,4-dithiadiphosphetane 2,4-disulfide] to convert ethyl benzenecarboxylate (ethyl benzoate) to ethyl benzenethiocarboxylate (ethyl thiobenzoate).

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