Phosphorus-Containing Dienophiles

Several structurally different types of phosphaalkenes containing a phosphorous-carbon double bond have been found to undergo [4 -I- 2] 

Entry Dienophile Diene Conditions Product(s) Yield Re 

It has been proposed that a phosphinidene sulfide, formed by magnesium metal reduction of a dichloro precursor, can be trapped by 2,3-dimethylbutadiene to yield an adduct [Eq. (11)].  

However, the initial Diels-Alder product was not isolated, but rather two further transformation products were. It was postulated that these species are artifacts produced during the workup procedure however, this interpretation has been questioned. 

The corresponding cycloarsanes undergo the same reaction in good yields [Eq. (14)1- 

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Phosphorus-Containing Dienophiles Phosphoalkenes and Related Compounds Other Dienophiles... 

Chirality in the phosphorus-containing dienophile induces a preferential mode of approach to the diene the (2R,45)-l,3,2-oxazaphospholidine 2-oxide 480 reacts with cyclopentadiene to give a 10 19 ratio (96% total yield) of the endo (structure confirmed by X-ray crystallography) and exo adducts, and a similar reaction with the IS, 45)-1,3,2-oxazaphospholidine 2-oxide gave endo and exo products in the ratio 2 3, with considerable diastereoisomeric excesses (80-88%) ... 

MO calculations at the MP4SDTP/6-311G //MP2/6-311G level on the Diels-Alder reaction of ethylene with l-phosphabut-3-en-l-yne show that the reaction is endothermic compared with the all-carbon case, which is exothermic.249 Ab initio studies have been presented for hetero-Diels-Alder reactions between phosphorus-containing dienes and dienophiles.250 Ab initio calculations on the Diels-Alder reaction between 21 /-phosphole and phosphaethene indicate that the reaction is concerted and synchronous.251 The Diels-Alder reaction between 1,3,5-triphosphabenzene and phosphaacetylene to form tetraphosphabarrelene was studied at the MP4SDQ/6-... 

We also consider new achievements in some classical cycloaddition reactions such as the Diels-Alder condensation with acetylenic dienophiles, [2-1-2] cycloadditions with acetylene component leading to creation of cyclobutene ring, and new results in cyclobutene syntheses by [2-1-2] acyclization of phosphorus containing 1,3-butadiene derivatives synthesized starting with propargyl-type alcohols. 

DMPP itself is not a reactive diene in Diels-Alder reactions,but it is activated by coordination to transition metal ions. Complex 198 contains a labile perchlorato ligand that is easily displaced by the dienophile, which possesses a coordinating atom (O, S, As or P) in the group E. The cycloaddition reaction occurs intramolecularly in a highly organised environment, which leads to the coordinated exo cycloadduct 199 exclusively. A standard decoordination step affords the desired enantiopure ligands 200. Only the exo-syn isomers are formed, which bear the lone pair at the phosphorus atom and the dienophile functionalities at the same side of the molecule. ... 

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