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Synthesis of New Chiral Derivatives of N,N'-Dimethylpropyleneurea (DMPU) and Examination of Their Influence on the Regio- and Enantioselectivity of Addition of 2-(1,3-Dithianyl)lithium to Cyclohex-2-en-1-one
- Source :
- Helvetica Chimica Acta; July 2002, Vol. 85 Issue: 7 p1999-2008, 10p
- Publication Year :
- 2002
-
Abstract
- The preparation of three new chiral derivatives of DMPU (N,N'-dimethylpropyleneurea) is described (Schemes 24); one type of derivative carries 1-phenylethyl or 1-cyclohexylethyl groups at the N-atoms of the tetrahydropyrimidin-2(1H)-one ring (2 and 4), another type of derivative is substituted at C(4) and C(6) of the heterocyclic ring (7). The potential of these chiral Lewis bases as promoters in the regio- and/or enantioselective addition of 2-(1,3-dithianyl)lithium to cyclohex-2-en-1-one was explored; they are all unable to effect enantioselective addition; the derivatives with branched substituents at the N-atoms do not shift the addition mode from 1,2 to 1,4, while the 3,4,5,6-tetrahydro-1,3,4,6-tetramethylpyrimidin-2(1H)-one does (Scheme 5). The results provide useful information regarding the nature of the nucleophilic organolithium reagent: obviously, the steric hindrance to Li complexation on the C&dbond;O O-atom of the tetrahydropyrimidin-2(1H)-one by branched substituents at N-atoms (cf. X-ray crystal structure of 2 in the Fig.) prevents solvent-separated-ion-pair (SSIP) formation; this was confirmed by PM3 and B3LYP/3-21-G(d)//PM3 calculations (Scheme 6).
Details
- Language :
- English
- ISSN :
- 0018019X and 15222675
- Volume :
- 85
- Issue :
- 7
- Database :
- Supplemental Index
- Journal :
- Helvetica Chimica Acta
- Publication Type :
- Periodical
- Accession number :
- ejs3631873
- Full Text :
- https://doi.org/10.1002/1522-2675(200207)85:7<1999::AID-HLCA1999>3.0.CO;2-K