Cyclopropyl-metal compounds, synthesis

A wide variety of organometallic methods of carbon-metal tr-bond formation3 have been employed in the synthesis of cyclopropyl-metal compounds. Consequently, with few exceptions the preparation of almost any main group or transition metal cyclopropyl compound has precedence in the literature. In this section only an overview, rather than a comprehensive survey, of the essential synthetic methods of cyclopropyl-metal com-... 

The important application of SPC in organic synthesis is their conversion into the gem-dimethyl group, which is a common fragment in many natural products as well as in synthetically made, physiologically active compounds. This transformation utilizes hydrogenation of the cyclopropyl fragment over a noble metal catalyst. Equation 20 presents a typical example of the introduction of the g m-dimethyl group into a complex molecule via a SPC intermediate ... 

Haloalkyl phenyl sulfides produce cycloalkyl phenyl sulfides on treatment with base. The synthesis of cyclopropyl phenyl sulfides has attracted particular interest since these compounds can be metal-lated - - by Bu"Li in THF and the resulting 1-phenylthiocyclopropyllithium has been used for spiro-annelation of various cycloalkanones. - Thus, 3-chloro-l-phenylthiopropane leads to phenylthiocyclopropane on reaction with potassium amide in liquid ammonia (Scheme 7, entry a), but attempts to prepare 2-methylcyclopropyl phenyl sulfide from 3-chloro-l-phenylthiobutane by an analogous route failed in the cyclization step. Neither 3-mesyloxy- and 3-tosyloxy-l-phenylthiododecanes " nor 3-tosyloxy-l-phenylthiobutane produce cyclopropane derivatives either on reaction with LDA in THF (Scheme 7, entry b). Failure in these ring closure reactions has been attributed to inadequate car-... 

Stoichiometric use of transition-metal-carbene complexes in organic synthesis has been thoroughly reviewed.Various examples using carbene complexes containing cyclopropane subunits have been reported.Here, the cyclopropyl moiety is either attached directly to the carbene carbon or is placed in a more remote position. This section only discusses isolated carbene complexes. Related transition-metal-catalyzed conversions of diazo compounds containing cyclopropane subunits, which are interpreted to proceed via carbene intermediates (e.g. ref 130), are not discussed here. 

The reaction of several a-diazoketones with ethyl vinyl ether under various conditions has been examined. In the presence of metal salts [Rh2(OAc)4, Pd(OAc)2, CuCl] ethoxy dihydrofurans are produced. The initial product of this reaction sequence is a cyclopropyl ketone which suffers from a spontaneous rearrangement to the dihydrofuran <96CJC2401>. An efficient synthesis of 3-acylfurans is achieved by Ag(I)/Celite mediated cycloaddition of dicarbonyl compounds with vinyl sulfide (<97TL5671> see also <97TL2095>). A two-step synthesis of 2-substituted 4-furanmethanol compounds was reported. The method involves a Homer-Wadsworth-Emmons reaction between 3-ketophosphonates and l,3-diacetoxy-2-... 

---