1,3-Cycloaddition diasteroselective

Stereoselective Diels-Alder reactions have been reported in several cases. Enantioselective Diels-Alder reactions of l-phenoxycarbonyl-l,2-dihydropyridine with 1-alkylated acryloyl-pyrazolidin-3-ones using a chiral cationic palla-dium-phophinooxazolidine catalyst afforded chiral isoquinuclidines with excellent enantioselectivity <2005TL5677>. Bismuth(lll) chloride-mediated diasteroselective intramolecular [4-f2] cycloaddition reactions of A-allyl derivatives of pyrazole aldehydes led to fused sulfur-containing pyrazole heterocycles <2003SC3063>. A highly diastereoselective intramolecular hetero-Diels-Alder approach toward tetracyclic pyrazoles from 5-(3-methyl-2-butenylthio)-3-methyl-l-phenyl-4-pyrazolecarboxaldehyde has been reported <1997SL1155>. 

A large amount of activity on 1,4-benzodiazepine derivatives was reported in 2004. Tetrahydro-l,4-benzazepin-2-one derivatives are of interest as P-turn peptidomimetics and their solid-phase synthesis was reported by Kim et al. <04JC0207>. The diasteroselective synthesis of two enantiopure tetrahydro-l,4-benzodiazepin-5-ones was also achieved based on intramolecular azide cycloaddition and subsequent stereoselective reduction of the 1,4-benzodiazepinone products <04TA687>. A different approach to tetrahydro-1,4-benzodiazepin-5-ones 80 involves the 1,2-thiazine 1-oxides 77 as key intermediates. These intermediates were then converted to the nitroaryl amides 78 (R , R, R = H or Me) which could be cyclised to 80 after hydrogenation of the nitro group via the intermediates 79 <04T3349>. 

As previously described (see section 2) the solvent dependence of ESIPT in flavonols has been found to play a key role in the reactivity of the photogenerated intermediates. Porco and co-workers reported that protic solvents such as 2,2,2-trifluoroethanol (TFE) are able to promote ESIPT pathway, leading to an increase of the population of the excited phototautomers (It) 119 7hus, the irradiation of 3-hydroxyflavone derivatives in chloroform/ TFE (TFE) 70 30 mixture and in the presence of methylcynnamate resulted in an improved cycloaddition yield (up to 55%) and diasteroselectivity (up to 5 1 d.r.). Furthermore, the use of protic TFE increased the photo-tautomerization yield, allowing the use of less reactive dipolarophiles including cinnamyl thioesters, amides or nitriles.The enanthioselective synthesis of potent cytotoxic (-)-Silvestrol (37) via TADDOL derivatives-mediated [3-1-2] cycloaddition has been reported. (Scheme 10). ... 

On the other hand, the use of the suitable combination of a metal salt, chiral ligand, and base promotes at low temperature the formation in situ of chiral A-metalated azomethine ylides from the corresponding iminoester and the subsequent selective cycloaddition onto the fullerene cage. Thus, the P,S chiral ligand Fesulphos along with copper(II) acetate directs the addition toward the formation of the stereoisomer (25, 55)-2-alkoxycarbonyl-5-arylpyrrolidino[3,4 l,2][60]fullerene with complete cis diasteroselectivity and enantiomeric excesses up to 93% (Scheme 34.9). 

The 1,3 dipolar cycloaddition between azomethine imines 47 and alkenes 48 delivers pyrazolidines 49 (Scheme 41.11). Highly diasteroselective and enantioselective versions of this cycloaddition have been developed by different research groups... 

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