Preparation and evaluation of N‐sulfinyl dienophiles for asymmetric hetero‐diels‐alder reactions

Abstract

S N R O + chiral Lewis acid CH 2 Cl 2 1c-i 3c-i 2 up to 97% ee S N R OA series of N-sulfinyl dienophiles 1c-i has been screened in asymmetric hetero-Diels-Alder reactions using chiral bis(oxazoline)copper(II) and -zinc(II) triflates. The survey pointed out N-sulfine 1c (R = P(=O)(OPh) 2 ) as the most promising N-sulfine regarding yield and stereoselectivity (up to 97% ee). The relative configurations, and in one case the absolute configuration, of the HDA adducts were established by X-ray analysis.selected to elucidate the scope and limitations of the asymmetric HDA reaction.

Cyclic Sulfinamides

“…Eventually, the method showed excellent endo/exo selectivity (> 95 : 5) and enantioselectivity (> 98 %) in the synthesis of bridged sultims 144 (selected examples are depicted in Scheme 61). [96][97][98][99] It should be noted, that contrary to bridged sultims 142 their higher homologues 144 are much more stable. They could be isolated without proceeding retro-Diels-Alder reaction and may be stored at rt without deterioration.…”

“…Eventually, the method showed excellent endo / exo selectivity (>95 : 5) and enantioselectivity (>98 %) in the synthesis of bridged sultims 144 (selected examples are depicted in Scheme 61). [96–99] …”

Update 1 of: C2-Symmetric Chiral Bis(oxazoline) Ligands in Asymmetric Catalysis

“…If the catalyzed reactions are performed under stoichiometric conditions, then excellent results in terms of yields and selectivity are obtained. However, when performed under catalytic conditions using 10 mol % of catalyst, then it is less selective, but with 1 equiv of trimethylsilyl trifluoromethanesulfonate (TMSOTf), it becomes strongly endoselective affording 347 with good to excellent enantiomeric excess (see Scheme and Table ). − The reaction is applicable to unusual N-substituents, and excellent enantioselectivities are obtained for both zinc(II) and copper(II) triflates …”

“…371À373 The reaction is applicable to unusual N-substituents, and excellent enantioselectivities are obtained for both zinc(II) and copper(II) triflates. 374 When the same N-sulfinyl amides 346 and acyclic dienes 348 are reacted with the Cu(OTf) 2 complex of box 1 as the catalyst in the presence of 1 equiv of TMSOTf, highly diastereoselective hetero DielsÀAlder reactions with cis-349 as the major isomer (Scheme 132) are the result. 373 To give an idea of the stereoselectivity of this reaction and the absolute configuration of the products, some selected examples are reported in Table 81.…”