Pyramidal carbon synthesis

In connection with the total synthesis of grandisol, an asymmetric addition of ethylene on chiral heterocyclic aminals and ketals was examined (Scheme 23). The selectivity can be high, with a preferred approach of ethylene from the less hindered side, especially when chiral pyrrolidone 97 or furanones 100 were used in place of cyclic enones [70]. The diastereoisomeric excess of 101 or 102 remains modest with 5-menthyloxy furanone, even if the dark addition of nucleophiles or radicals on 100 occurs with a total facial selectivity. From a detailed analysis of the dependence of the product ratio with temperature and substituents, it was proposed that a pyramidalization of the (3-carbon in the relaxed of the... 

Most alkyl carbanions undergo facile pyramidal inversion. Cyclopropyl anions are an exception, presumably because the transition state, with a planar trigonal carbon, is more strained than the ground state. The configurational stability of cyclopropyl anions is of value in the synthesis of deuterated cyclopropanes by the Haller-Bauer reaction (see Section II.B). An interesting dilemma arises when a cyclopropyl anion is stabilized by a n-electron acceptor substituent such as a nitrile or an ester. Will the anion then retain its pyramidal equilibrium geometry for the strain reasons alluded to above, or will it become planar in order to maximize overlap of the filled orbital on carbon with the n orbital of the substituent Walborsky and coworkers addressed this question in a series of experiments in which rates of H/D exchange and racemization were compared for an optically active cyclopropane exposed to a base in a deuterated hydroxylic solvent. The outcome can be illustrated with the particular example of 1,1-diphenylcyclopropane-2-... 

For the acetylenic sulfoxide, because of its configurationally stable pyramidal stereogenic sulfur atom (a lone electron pair, an oxygen and two different carbon substituents), it can exist in chiral forms. Therefore, in chiral acetylenic sulfoxide, the sulfoxide moiety not only serves as a chemical activator of the acetylene unit, it can also induce stereochemical control at the adjacent carbon centers to achieve enantioselective synthesis. In this article, we shall discuss the preparation of these a, /J-unsaturated synthons and their applications in Diels-Alder reactions, heterocycle and alkaloid syntheses. 

PCI3 r.d. 1.57 m.p. -112°C b.p. 75.5°C. it is soluble in ether and in carbon tetrachloride but reacts with water and with ethanol, it may be prepared by passing chlorine over excess phosphorus (excess chlorine contaminates e product with phosphorus(V) chloride). The molecule is pyramidal in the gas phase and possesses weak electron-pair donor properties, it is hydrolysed violently by water to phosphonic acid and hydrogen chloride. Phosphorus(lll) chloride is an important starting point for the synthesis of a variety of inorganic and organic derivatives of phosphorus. 

The FVP synthesis of circumtrindene (155) was conducted with decacyclene (154, X=H) at 1,250 °C, but this protocol gave the product in very low yield (Scheme 48) [165] because unfunctionalized aryl carbon atoms are inefficient for C-C bond formation. Trichlorodecacyclene 154 (X=C1) dramatically improves the yield of 155 up to 27% [166]. Based on crystallographic analysis, the depth of the bowl is 3.107 A and the POAV pyramidalization angles of the central hexagon are 11.9° and 12.4° [167]. 

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