Majetich synthesis

Majetich G., Hicks R. Applications of Microwave-Accelerated Organic Synthesis... 

A B-ring-last-strategy was applied by Majetich and coworkers for their synthesis of the natural ( )-l(15),8-dolastadien-2-ol ( )-107 (desoxyisoami-jiol, 1991) [87, 88]. A Lewis acid mediated intramolecular allylsilane 1,6-ad-dition of the dienone 157 afforded the 5,7,6-tricyclic carbon framework of the dolastanes (158) (Scheme 25). The missing carbon atom was intro-... 

Scheme 25 Total synthesis of ( )-l(15),8-dolastadien-2-ol (rac-107, desoxyisoamijiol) according to Majetich (1991)...

The synthesis of 3,7-dimetyhl-6-hydroxy-8-methoxyisochroman (4) and its ester and ether derivatives. (From Cutler, H. G., Majetich, G., Tian, X., and Spearing, P., /. Agric. Food Chern., 1997, 45, 1422. With permission.)... 

Giguere, R.J., Bray, T.L., Duncan, S.M. and Majetich, G., Application of commercial microwave Ovens to organic synthesis, Tetrahedron Lett., 1986, 27, 4945. 

Majetich reports a general intramolecular Lewis acid allylation protocol for the synthesis of bicy-clo[5.4.0]undecen-3-ones (168) and bicyclo[4.4.0]decen-3-ones (170), which are 1,6-addition products (Scheme 27). The same precursors, (167) and (169), when submitted to the fluoride ion cyclization protocol, also afford 1,2- and 1,4-addition products.73 Typically, ethylaluminum dichloride, a proton sponge Lewis acid, is used in order to minimize adventitious protonic desilylation. Other 0,y-unsatu-rated silanes also undergo similar intramolecular Lewis acid catalyzed additions for example, the si-lylpropargylic enones (171) undergo intramolecular cyclization to the allenylspiro system (172).74... 

G. Majetich, in Organic Synthesis, Theory and Applications, (Ed. T. Hudlicky), JAI Press, Greenwich, CT, 1989. 

Majetich et al [81] have reported an excellent synthesis of miltirone (197) using cyclialkylation-based strategy. This is described in Fig. (26). 

As the key precursor towards the realization of 1,7-epoxy cyclononanes and 1,8-epoxycyclodecanes, an 1 l-oxatricyclo[6.2.1.02,6]decane skeleton was constructed by using the Hoffmann [4+3] cycloaddition methodology <07EJO4383>. In Majetich s total synthesis of (-)-salviasperanol, the key step was the trifluoroacetic acid-promoted isomerization of a vinyl epoxide to 2,5-dihydrofuran, whose O-thiocarbamate was removed by radical reaction to produce salviasperanol dimethyl ether <07OL85>. The synthetic route is depicted below. 

In the stereoselective total synthesis of ( )-14-deoxyisoamijiol by G. Majetich et al., the last step was the epimerization of the C2 secondary allylic alcohol functionality. The Mitsunobu reaction resulted only in a poor yield (30%) of the inverted product, so the well-established sulfoxide-sulfenate rearrangement was utilized. The allyic alcohol was first treated with benzenesulfenyl chloride, which afforded the thermodynamically more stable epimeric sulfenate ester via an allylic sulfoxide intermediate. The addition of trimethyl phosphite shifted the equilibrium to the right by consuming the desired epimeric sulfenate ester and produced the natural product. 

P CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Tomas Hudlicky. Asymmetric Diels-Alder Reactions, Michael J. Tasihner. Nonconventional Reaction Conditions Ultrasound, High Pressure, and Microwave Heating in Organic Synthesis, Raymond J. Giguere. Allylsi-lanes in Organic Synthesis, George Majetich. 

Giguere RJ, Bray TL, Duncan SM, Majetich G (1986) Tetrahedron Lett 27 4945 Loupy A, Petit A, Hamelin J, Texier-Boullet F, Jacquault P,Mathe D (1998) Synthesis, 1213 Villemin D, Thibault-Starzyk F (1991) J Chem Educ 346 Jacquault P (1992) EU Patent 545995 AI Prolabo Co... 

Kirkpatrick EM, Majetich SA, McHenry ME. 1995. Synthesis, structure, properties and magnetic apphcations of carbon-coated nanocrystals produced by a carbon arc. Mater Sci Eng A 204 19-24. 

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