Synthesis and X-Ray Structure of Bis{S-(1-lithio-3,3-diphenylprop-2-enyl)-N-methyl-S-phenylsulfoximine– Tetrahydrofuran (1/2)} Complemented by Model ab initio Calculations of α-Lithiosulfoximines

✍ Scribed by Jürgen F. K. Müller; Bernhard Spingler; Margareta Zehnder; Rohit Batra

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: German
• Weight: 355 KB
• Volume: 79
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19960790324

✦ Synopsis

Abstract

The gas‐phase structure of N,S,S‐trimethylsulfoximine 1 and of its monolithiated isomers 2–4 was calculated by ab initio methods. It was found that a LiCSN four‐membered chelate 2 is the most stable isomer. The second minimum 4 shows NLiO complexation and is only slightly higher in energy. Li‐Contacts with the C(α) atom and the sulfoximine O‐atom in 3 are energetically disfavored by 6.1 kcal/mol. The two transition states 5 and 6 suggest an interconversion mechanism of 2 to 3 with 4 as an intermediate. A comparison of 4 with the crystal structure of the THF solvate 7, which was prepared by the addition of BuLi to (±)‐S‐(3,3‐diphenylprop‐2‐enyl)‐N‐methyl‐S‐phenylsulfoximine (8) at low temperature in THF, demonstrates that the coordination geometry in the solid state is in good agreement with the calculated structure. The (1‐lithioallyl)sulfoximine 7 crystallized as a centrosymmetric dimeric aggregate featuring an eight‐membered ring with the atomic sequence (LiNSO)~2~. The O‐atoms of two THF molecules and the sulfoximine O‐ and N‐atoms are coordinated to the Li‐atom in a tetrahedral orientation. After metallation, a significant shortening of the SC(α) bond is observed. Remarkably, only one of the two possible diastereoisomeric enantiomer pairs is found in the solid state.