ISSN:
1434-193X
Keywords:
Ylides
;
Wittig olefination
;
Reaction mechanism
;
Phosphorus-carbon coupling constants
;
Substituent perturbation
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Reaction of the ylide (cyclopropyl)3P=CH2 with Michler's thioketone S=C(C6H4NMe2)2 in [D5]pyridine gave the thio Wittig intermediate [(cyclopropyl)3P+-CH2-CAr2-S-] (11; 31P NMR: δ = +27.7). Compound 11 was characterized by X-ray diffraction and shown to exhibit a gauche-betaine-type structure with an S-C-C-P dihedral angle of 52.9(3)° and a P···S separation of 3.312(2) Å. The characteristic averaged 1JPCipso(aryl) coupling constant was used to elucidate the characteristic structural properties of Wittig and thio Wittig intermediates derived by treatment of the series Ph3P=CH2 (2a), Ph2MeP=CH2 (2b), and PhMe2P=CH2 (2c) with bis(p-methoxyphenyl) ketone to give 3 or benzophenone (to give 3′) or bis(p-methoxyphenyl) thioketone (to give 5), respectively. The oxaphosphetane series 3′a-3′c shows a strong response of the 1JPCipso(aryl) values (3a: 94 Hz; 3′b: 74 Hz; 3′c: 47 Hz) to this substituent perturbation, as it is expected for a dynamic trigonal-bipyramidal situation at the phosphorus atom, whereas the thio Wittig intermediate is only very little affected [1JPCipso(aryl) of 5a: 92 Hz; 5b: 86 Hz; 5c: 82 Hz]. Thus, the thio Wittig intermediates 5 seem to exhibit a pronounced phosphonium character in polar solvents and may be regarded as thiabetaine-type intermediates in solution.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
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