Stereoselective cyclopropanation

Hodgson very recently reported an efficient intramolecular and completely dia-stereoselective cyclopropanation of bisliomoallylic and trisliomoallylic epoxides based on the use of a-lithiated epoxides. In a seminal paper, Crandall and Lin had reported that the reaction between t-BuLi and l,2-epoxyhex-5-ene (100) gave, inter alia, small amounts oftrans-bicyclo[3.1.0]hexan-2-ol (102, 9%) (Eq. a, Scheme 8.28)... 

Another example is the asymmetric synthesis of ( )-pinidine 208 and its isomers. These syntheses are achieved via asymmetric enolization, stereoselective cyclopropanation, and oxidative ring cleavage of the resulting cyclopropanol system (Scheme 5-68).123... 

The key problem in the preparation of 296, 297 undoubtedly is the stereoselective assembly of the chains of four to five contiguous cyclopropyl groups. The strategies of all total syntheses known so far rely on auxiliary-directed stereoselective cyclopropanations of double bonds [111a, 163,164]. The chemistry of bicyclopropylidene (1), namely its capability to be functionalized (Schemes 8, 9), dimerized (Scheme 15), and stereoselectively reduced (Scheme 53) opens up new perspectives to approach the assembly of quatercyclopropyl derivatives. 

Section 14.2 describes the highly stereoselective cyclopropanation chemistry of the donor/acceptor-carbenoids (Fig. 14.1a) [16]. This section introduces the range of vinyl, aryl, alkynyl, and heteroaryl functionalities that have been used as donor groups in this chemistry. Also, chiral auxiliaries and chiral catalysts that achieve high asymmetric induction in this chemistry are described [25]. The next two sections cover chemistry that is unique to the vinylcarbenoid system, namely [3-t4] cycloaddition with dienes (Fig. 14.1b see also Section 14.3) [13] and [3-1-2] cycloaddition with vinyl... 

A series of axially chiral bis(oxazolines) 58a-n were prepared by Rippert for stereoselective cyclopropanation studies.The use of Burgess reagent proved to be superior than other reagents such as PPha/CCLt/MeCN or MsCl/Et3N/CH2Cl2 (Scheme 8.22). 

Dihydro-2//-pyran also undergoes a highly stereoselective cyclopropanation reaction with methyl l-(tri-isopropylsiloxy)vinyldiazoacetate in the presence of a chiral rhodium catalyst. Optically active furo[2,3- 5 ]pyran derivatives are generated upon desilylation of the cyclopropanes (Scheme 40) <2005SL1397>. 

H. Lebel, J.-F. Marcoux, C. Molinaro, and A. B. Charette, Stereoselective Cyclopropanation... 

D. Stereoselective Cyclopropanation of Alkenes using Chiral Auxiliaries. . . 266... 

The stereoselective cyclopropanation of chiral alkenes can be divided into two classes cyclic and acyclic alkenes. Furthermore, within each class, a subdivision exists involving those that contain a proximal basic group that can direct the cyclopropanation reaction of zinc carbenoids and the others that do not. The discrimination of reactivity between alkenes that possess a proximal basic group and those that do not was first highhghted early on when Simmons and Smith noticed that the cyclopropanation of l-(o-methoxyphenyl)-l-propene was more efficient than that of the related meta and para isomers (equation 46). ... 

Cyclopropanation mediated by zinc organometallics 2. Stereoselective cyclopropanation of acyclic alkenes... 

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