Torgov reaction

Further application of the Torgov reaction has been made in the synthesis of oestrone, the 3,16-dimethylether of oestriol, and a series of 4-halogeno-oestrogens. A novel modification involves the use of allylic amine (412) (readily prepared from the enamine of m-methoxytetralone) in place of the usual alcohol... 

As an example of a steroid total synthesis, the industrial procedure used to make norgestrel, the gestagen used in many contraceptives, is sketched here. Its basis is the Torgov reaction, a variation of the Robinson annelation, which mns essentially neutral media. The carbanion of 1,3-dioxo compounds adds to allylic alcohols, e.g., 2-ethylcyclopentanol-1,3-dione, under weakly basic conditions. Both the dione and the styrene double bond are stable under these conditions. Regio- and stereoselective microbial reduction of one of the keto groups, acid-... 

Total Synthesis - A major effort vra.s devoted to developing and disproving the original Smith-Torgov reaction sequence leading to estrapentaenes of type XIII. 

Torgov introduced an important variation of the Michael addition allylic alcohols are used as vinylogous a -synthons and 1,3-dioxo compounds as d -reagents (S.N. Ananchenko, 1962, 1963 H. Smith, 1964 C. Rufer) 1967). Mild reaction conditions have been successful in the addition of ],3-dioxo compounds to vinyl ketones. Potassium fluoride can act as weakly basic, non-nudeophilic catalyst in such Michael additions under essentially non-acidic and non-basic conditions (Y. Kitabara, 1964). 

In the first of these sequences, often called the Torgov-Smith synthesis, the initial step consists in condensation of a 2-alkyl-cyclopentane-l,3-dione with the allyl alcohol obtained from 6-methoxy-l-tetralone and vinylmagnesium chloride. Although this reaction at first sight resembles a classic SN displacement, the reaction is actually carried out with only a trace of base. 

Chiral titanium complexes are also employed as effective asymmetric catalysts for other carbon-carbon bond-forming reactions, for example addition of diketene (Sch. 66) [154c,162], Friedel-Crafts reaction (Sch. 67) [163] (Sch. 68) [164], iodocar-bocyclization (Sch. 69) [165], Torgov cyclization (Sch. 70) [166], and [2 -i- 1] cycloaddition (Sch. 71) [167]. Asymmetric functional group transformations can also be catalyzed by chiral titanium complexes. These transformations, for example the Sharpless oxidation [168] or hydride reduction [169] are, however, beyond the scope of this review because of space limitations. Representative results are, therefore, covered by the reference list. 

A new angular methylation procedure, at Cis, involving the Simmons-Smith reagent was discovered, thus extending the usefulness of the Smith-Torgov total synthesis of 19-norsteroids. The preparation and properties of 5,19-cyclosteroids was the subject of several studies.Interestingly enough, the Villsmeier reaction on enamines of 3-heto-A -steroids led to the 1,6-diformyl derivatives. ... 

Nazarov, I. N. Torgov, I. B. Terekhova, L. N. Bull. Acad. Sci. (USSR) 1942, 200. I. N. Nazarov (1900—1957), a Soviet Union Scientist, discovered this reaction in 1942. It was said that almost as many young synthetic chemists have been lost in the pursuit of an as)Tnmetric Nazarov cychzation as of the Bayliss—Hillman reaction. 

It was reported that chiral oxazaborolidine, prepared from the reaction of n-BuBCl2 with (S)-l,l-diphenylpyrrolidinemethanol, can be obtained in high purity (Scheme 23.38). A catalyst prepared in this way was used in the reduction of the Torgov diketone with catecholborane and yielded the hydroxy ketone in 87% yield and 92% ee. Based on this observation, the role of additive N,N-diethylaniline was clarified. ... 

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