Methyl pyridyl sulfoxide

Demailly and coworkers195 found that the asymmetric induction increased markedly when optically active methyl pyridyl sulfoxide was treated with an aldehyde. They also synthesized (S)-chroman-2-carboxylaldehyde 152, which is the cyclic ring part of a-tocopherol, by aldol-type condensation of the optically active lithium salt of a,/3-unsaturated sulfoxide. Although the diastereomeric ratio of allylic alcohol 151 formed from lithium salt 149 and 150 was not determined, the reaction of 149 with salicylaldehyde gave the diastereomeric alcohol in a ratio of 28 72196. 

Heterocyclic amines have also been used as phase transfer catalysts. However, because these amines quaternize easily, the question is whether the operative catalyst is the tertiary amine or the quaternary ammonium salt formed in situ Furukawa et al.286 have shown that a methyl 2-pyridyl sulfoxide may be used as a phase transfer catalyst and promote substitution reactions between lithium chloride or sodium cyanide and benzyl bromide. According to the authors, the catalyst behaves as a cation complexer and not as a quaternary ammonium salt formed in situ by a Menschutkin reaction. 

The adducts resulting from Diels-Alder reaction of pyridyl sulfoxides with furan have been used in the synthesis of a number of natural products. Thus, a new procedure for the total synthesis of optically actives C-nucleosides was reported by Koizumi et al. [38], who prepared D-showdomycin (19) and (D)-3,4-0-isopropylidene-2,5-anhidroallose (20) from the endo(t) 18a adduct (Scheme 10). (-i-)-Methyl 5-epishikimate (21) [39] and pentaacetyl- -D-mannopyranose (22) [40] were also obtained starting from endo(t) 18a (Scheme 10), the cleavage of the oxygenated bridge being the key step of these transformations. 

Oae et al. reported the use of methyl 2-pyridyl sulfoxide (582) as an excellent phase transfer catalyst (PTC) promoting simple 8, 2 reactions of alkyl halides. One of the best results is shown in Scheme 7.93 [364]. 

Oxidation of 7-hydroxy- and 7-aryl-5-oxo-2,3-dihydro-5//-pyrido[l,2,3- f< ]-l,4-benzothiazine-6-carboxylates and 6-carboxamides with 3-chloroper-oxybenzoic acid in CH2CI2 yielded sulfoxides and sulfones, depending on the molar ratio of the substrate and oxidizing agent (00MIP7). A sulfoxide was prepared by the oxidation of ethyl (3S)-3-methyl-10-(2,6-dimethyl-4-pyridyl)-7-oxo-2,3-dihydro-7//-pyrido[l,2,3-<7c]-l,4-benzothiazine-6-carbox-ylate (OOMIPIO). 

Sundell G, Sjostrand SE, Olbe L. Gastric antisecretory effects of H83/69, a benzi-midazolyl-pyridyl-methyl-sulfoxide. Acta Pharmacol. Toxicol., 1977, Suppl. 4, 77. 

In 1972, Tsuchihashi disclosed that the carbanion (28 Ar = p-tolyl), generated from (/ )-methyl p-tolyl sulfoxide with lithium diethylamide, adds to benzaldehyde or a-tetialone to give an adduct (29) in a dia-stereomeric ratio of 50 50 or 64 36, respectively. Additions of this carbanion to various unsymmetrical ketones are also reported to be poorly diastereoselective (for example, EtCOMe 50 50, Bu COMe 55 45, Bu COPh 70 30). Note that in the case of Ar = 2-pyridyl a chiral sulfinyl group increases the asymmetric induction observed in the addition of the corresponding carbanion to carbonyl compounds (PhCHO 80 20, R-C9H19CHO 70 30). Since diastereomer pairs of (29) are separable, chromatographic separation followed by reductive desulfurization with Raney Ni provides a method for obtaining optically active alcohols (30 Scheme 9). 

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