4-Phenyl-1,2,4-triazoline-3,5-dione PTAD

Methyl-3-(tetramethylcyc opropylidene)propene (176), obtained by isomerization of allene 175 with potassium ferr-butoxide, added to 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD, 177) at room temperature to give the Diels-Alder adduct 178 in 46% yield (Scheme 26) [43]. 

Scheme 18 Separation of zingiberene from ginger oil using a selective and reversible Diels-Alder reaction with phenyl l,2,4-triazoline-3,5-dione (PTAD) [105]...

The (diphenylmethylene)aminocyclobutenecarboxylates 109 obtained by rearrangement of the DMPA-H adducts of 1-Me, 2-Me, contain a 2-azadiene unit and a cyclobutene moiety. Indeed, the parent compound 109 a reacted with 4-phenyl-l,2,4-triazoline-3,5-dione (PTAD, [80]) at room temperature in a [4-1-2] cycloaddition mode to yield the tricyclic tetraazaundecene 132 in almost quantitative yield (Scheme 44) [8]. As substituted cyclobutenes, compounds 109 should be capable of opening up to the corresponding butadienes [1, 2b, 811. When compounds 109 were subjected to flash vacuum pyrolysis, the dihydro-isoquinolines 135 were obtained, presumably via the expected ring-opened intermediates 133, which subsequently underwent bn electrocyclization followed by a 1,5-shift, as is common for other 3-aza-l,3,5-hexatrienes [82]. 

Dimethyloxazolidines have been utilized as chiral auxiliaries for the diastere-oselective functionalization of the optically active tiglic acid derivatives by means of epoxidation with dimethyldioxirane (DMD) or m-CPBA and ene reactions with 02 or 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD). In the DMD and m-CPBA epoxidations, high diastereoselectivities but opposite senses of diastereomer selection was observed. In contrast, the stereochemistry of the 102 and PTAD ene reactions depended on the size of the attacking enophile whereas essentially perfect diastereoselectivity was obtained with PTAD, much lower stereoselection was observed with 02. The stereochemical results for the DMD and m-CPBA epoxidations and the PTAD ene reaction are explained in terms of the energy differences for the corresponding diastereomeric transition states, dictated by steric and electronic effects.200... 

H and 13C KIEs were determined for the ene reaction of 4-phenyl-l,2,4-triazoline-2,5-dione (PTAD) with 2-methyl-2-butene 44 or 2-methyl-l-pentene 45 (Scheme 7).91 Authors assumed that although in the reaction of 2-methyl-l-pentene two products are formed, reactions should proceed via very similar transition states in the first mechanistic step. 

A novel route to the ring b aromatic anthrasteroids (49) from S,7-dienes (50) proceeds in two steps and uses 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) as the oxidant, as is shown in equation (47)7 Addition of PTAD to the steroidal S,7-diene gives an adduct which, when treated with boron trifluoride etherate, rearranges to the anthrasteroid in generally greater than 90% yield. This reaction presumably proceeds through a spirocyclohexa-1,4-diene. 

A [2 + 2] cycloaddition occurred on reaction of 4-phenyl-4//-l, 2,4-triazoline-3,5-dione with vinylcyclopropane (1) or 2-oxabicyclo[3.1.0]hex-3-ene (3). The yields of products 2 and 4 were excellent, and the cycloadduct 4 was formed as a single (cw-a t/-< w)-isomer. Formation of both adducts is, in fact, noteworthy since 4-phenyl-4//-l,2,4-triazoline-3,5-dione (PTAD) reacts in different ways with other alkenes, and 2-oxabicyclo[3.1.0]hex-3-ene undergoes [(2 + 2J + 2J cycloadditions with maleic anhydride and tetracyanoethene. " ... 

Phenyl-l,2,4-triazoline-3,5-dione (often PTAD or Cookson s reagent ) is a highly reactive dieno-phile it has often been used to trap nnstable dienes or characterize dienes as adducts. Two examples of its reactivity are shown below. 

The most frequently used l,2,4-triazoline-3,5-diones include 4-methyl-l,2,4-triazoline-3,5-dione (MTAD) (2) and 4-phenyl-l,2,4-triazoline-3,5-dione (PTAD) (3), also called the Cookson reagent. Many other substituted derivatives of PTAD are also known but not widely used. A similar situation is found with some bifunctional compounds 4, where X can be aliphatic, aromatic, or a combination of aromatic and aliphatic parts [72M11 78CB3519 79MI1, 79MI2 85MI1 87JPS(A)2781],... 

By far the most widely used starting material for side chain elaboration schemes has been the C-22 aldehyde. This compound, readily obtained from the ozonolysis of sigmasterol i-ether or the 4-phenyl-l, 2,4-triazoline-3,5-dione (PTAD)-diene adduct of ergosterol has been modified in a number of ways. 

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