Seyferth reagents

Catalyst-mediated decomposition of diazo compounds in the presence of C=S compounds has found application for the preparation of thiiranes in homogeneous systems (68,110,111). Recently, a convenient procedure for the preparation of geminal dichlorothiiranes from nonenolizable thioketones and chloroform under Makosza conditions was reported (112). Another approach to 2,2-dihalogenated thiiranes (e.g., 2,2-difluoro derivatives) involves the thermolysis of Seyferth reagents in the presence of thioketones (113,114a). Nucleophilic dimethoxycarbene was shown to add smoothly to adamantanethione to provide a unique approach to a thiiranone (5, 5 )-dimethylacetal (114b). 

The observation that phenyl(trichloromethyl)mercury undergoes dissociation at 150 °C to give phenyl-mercury(II) chloride and dichlorocarbene has led to a wide range of organomercury compounds (PhHgCX3 — Seyferth reagents)15-18 which serve as efficient dihalocarbene transfer reagents (equation... 

Seyferth reagents are ideal for the dihalocyclopropanation of deactivated or base sensitive substrates such as allyl halides, allyl isocyanates, polychloroalkenes, a, 3-unsaturated ketones, esters, nitriles and sulfones.19... 

We have already seen the bishydroxylation using 0s04 and NMO this time lead tetraacetate is used to cleave the diol and yield the aldehyde. The phosphorane (Me0)2P(0)CHN2 is named the Gilbert-Seyferth reagent. 8 It basically behaves like the phosphoranes in the Horner-Wadsworth-Emmons reaction described above, except that the olefin subsequently loses nitrogen, creating the desired triple bond (also see Chapter 10). 

Explain the role of the Seyferth reagent in the formation of product 6. What is the mechanism of this step ... 

Dichlorocarbene, generated in situ from an organomercury precursor, phenyl(bromo, dichloromethyl)mercuiy (Seyferth reagent), adds to polybutadiene in a similar maimer [56]. The reactions take place under homogeneous conditions. They can be carried out aal% solutions of the polymer in benzene, using 10-20% mol excess of the reagent. 

Faster-reacting than other Seyferth reagents 1-4 days at room temperature and 1-10 min at 80°. 

Seyferth prepared a-halogenoalkyl-lithium and -magnesium compounds by treating the appropriate gem-dihalides with butyllithium or with Grignard reagents at low temperature, and then used the products to prepare acyclic and cyclic a-halogenoalkyltin compounds (57-60). Typical examples are shown in the following equations. 

D. Seyferth, ed., New Applications of Organometallic Reagents in Organic Synthesis. Elsevier, Amsterdam, 1976. 

Finally, it should be mentioned that from a purely synthetic point of view the reactions involving "transfer" of methylene groups -like the Simmons-Smith reaction [27] or Seyferth s reagents [28]- may be considered formally as cheletropic additions of a [2 + 1] type. 

Studies by the submitters have indicated that the procedure reported here is the preferred method for the preparation of bicyclo[3.2.1]octan-3-one. It employs readily available, inexpensive reagents, and the overall yield is good. In addition, the method can be used for the synthesis of the difficultly accessible next higher homologues of bicyclo[2.2.2]oct-2-ene as well as for derivatives of norbornene. Bicyclo[3.2.2]nonan-3-one and l-methylbicyclo[3.2.1]octan-3-one have been prepared by a similar route6 in 60% and 47% yields, respectively (based on adduct). However, the preferred procedure for the formation of the dichlorocarbene adduct of bicyclo[2.2.2]oct-2-ene is that of Seyferth using phenyltrichloromethylmercury. Even in this case the overall yield is moderate (37%). 

Direct Nucleophilic Acylation by the Low Temperature, in situ Generation of Acyllithium Reagents a-Hydroxyketones from Ketones Synthesis of 3-Hydroxy-2,2, 3-trimethyloctan-4-one from Pinacolone R. Hui and D. Seyferth, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139... 

Hui, R. Seyferth, D. Direct nucleophilic acylation by the low-temperature, in situ generation of acyllithium reagents a-hydroxy ketones from ketones 3-hydroxy-2,2,3-trimethyloctan-4-one from pinacolone. Org. Synth. 1993, Coll. Vol. VIII, 343-346. 

Seyferth, D. Weinstein, R. M. Hui, R. C. Wang, W.-L. Archer, C. M. Synthesis of a-hy-droxy ketones by direct, low-temperature, in situ nucleophilic acylation of aldehydes and ketones by acyllithium reagents./. Org. Chem. 1992, 57, 5620-5629. 

Chemical Modification. Reactions on the macromolecular polyenes were carried out by procedures described previously (3, 4). PhHgCBr3 is obtained by a modification of Seyferth s method (21) from PhHgBr and HCBr3 in presence of a base. Yields similar to those reported in the literature are obtained more easily by replacing the complex (tert-BuOK— tert-BuOH) with a solution of sodium tert-amylate in benzene as prepared by Conia (24). This reagent was, in fact, used systematically in place of potassium tertf-butylate it is easier to use and can be prepared completely free of alcohol. 

The products C are obtained by reduction of products B (X = Br) by Seyferth s method using Bu3SnH at 80°C. (24). This conversion gives yields of more than 95% in the presence of an excess of hydride. The same reaction with B (X = Cl) at 140°C. only results in the reduction of one halogen by using other reagents such as Ph3SnH the same result is obtained, but lower temperatures are possible (i.e., about 100°C.). 

---