Synthesis of Three-Membered Rings

SYNTHESIS OF THREE-MEMBERED RINGS WITH TWO HETEROATOMS... 

This chapter will deal exclusively with three-membered rings containing the hetero atoms O, S and N, and fused to the steroid skeleton. Because of the conformational requirements in steroids, not all of the usual methods of synthesis of three-membered rings are applicable to the fused ring system. For the synthesis of steroids to which an aziridine, oxirane or thiirane is attached either in the side chain or at a ring position but not directly fused to the nucleus, the methods discussed in this chapter, as well as others, are applicable. 

D. The Synthesis of Three-membered Ring Sulfones and Sulfoxides.. . ... 

In the last chapter we met diazoalkanes as sources of carbenes in the synthesis of three-membered rings. These same diazoalkanes are useful reagents for rearrangements via carbenes or carbocations. 

Synthesis of Three-Membered Rings with One Silicon Atom... 

Synthesis of Three-Membered Rings with One Germanium or Tin Atom 1.09.7.1 Ring Formation by [2+1] Cycloaddition... 

Unfortunately, in all of the known cases reductive cyclization with, e.g., lithium naphtalide was necessary to obtain the products. With this route the synthesis of three-membered rings containing various group 14 metals is limited and yields are poor. In contrast, reaction of 2 equiv. of tris(trimethylsilyl)silyllithium with GeCb at -78 C yields (Me3Si)2Si 2Ge(SiMe3)2 (3) in a straightforward way [9] (Fig. 4). 

Synthesis of Three-membered Rings Containing Highly Coordinate Selenium Atom 275... 

A possible synthesis of three-membered ring compound (28) is by intramolecular Friedel-Crafts reaction on acid chloride (29) and some chemists wished to investigate this possibility. They first had to synthesise... 

Miscellaneous Reactions of Methylenephosphoranes.—The synthesis of three-membered rings by means of phosphorus ylides has been reviewed and there have been several new reports of this type of reaction. Optically active a,p-un-saturated esters have been converted into cyclopropanes highly stereoselectively by reaction with isopropylidenetriphenylphosphorane as the key step in syntheses of both (li ,3 )-chrysanthemic acid methyl ester (53) and the (IR) cis-gem dibromovinyl analogue (54). The addition of reactive phosphonium ylides to functionalized 1,3-butadienylphosphonates provides a new synthesis of 2-cyclopen ten-1 -ylphosphonates (5 5). ... 

H. J. Bestmann, G. Schmid, and L. Kisielowski, Synthesis of Three-Membered Rings by Means of Phosphorus Ylides , Isr. J. Chem., 1982,22,45. 

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