Homer selectivity

Dienes. The Homer- /-selective. However, differt allylphosphonates, and therefor proup is critical. Thus, NaH -BuOK for those beann r rntamethyldiethylenepentamin... 

In the other approach, again harmalane (150) was treated with methyl 2-(di-ethylphosphono)acrylate (174), resulting in iminophosphonate 175. By its sodium borohydride reduction and subsequent lactonization, the amidophospho-nate 176 has been obtained, Wittig-Homer reaction of 176 with acetaldehyde followed by selective reduction of the carbonyl group of the enamide function supplied ( )-deplancheine in good yield (116). 

M. W. Homer, L. Hough, and A. C. Richardson, Selective benzoylation of methyl 2-benzamido-2-deoxy-a-D-glucopyranoside A convenient preparation of derivatives of 2-amino-2-deoxy-D-galactose, /. Chem. Soc., Sect. C (1970) 1336-1340. 

Secondary alcohol 11 is first protected as a silyl ether with TBS chloride, after which the terminal double bond is ozonized. The resulting methyl ketone is subsequently converted stereoselectively with a Homer-Wadswonh-Emnions reaction21 into olefin 13. This reaction sequence leads to tram selectivity in the formation of the terminal double bond in 13. 

The Wollcnherg method was used to construe the sensitive -polyene structure of roflamycoin A variation on the Homer-WaJsworth-Lmmons reaction was selected for the maerocyclization, since the possibility for macrolacto-ni/ation — an obvious approach for a luctnne — is ruled out due to steric hindrance from the isopropyl group in the position (C-35) adjacent to the lactone functionality... 

Homer-Wadsworth-Emmons reactions of ketones and aldehydes with phosphono-acetate esters, (R20)2P(=0)CH2C02R1, produce E/Z mixtures of a, /Tunsaturated esters. Use of the conventional reagent, sodium hydride, gives some selectivity. The combination of tin(II) triflate and A -cthylpipcndine enhances—and sometimes also reverses—the selectivity in most cases studied.71 Six-membered oxo-coordinated tin intermediates are proposed to control the selectivities observed. A similarly selective synthesis of trisubstituted exocyclic alkenes from cyclic ketones has been reported.72... 

Carbocyclic brighteners gained new impetus after 1959, when the trialkylphos-phite-activated ethylenation process developed by Homer became available [27], This process, which features a high yield and high selectivity for the E isomers needed for optical brighteners, is extremely interesting from an industrial point of view. The principal products are distyrylarenes and divinylstilbenes, which have retained their importance to the present day. 

Lee CG, Homer RJ, Zhu Z, Lanone S, Wang X, Koteliansky V, Shipley JM, Gotwals P, Noble P, Chen Q, Senior RM, Elias JA. Interleukin-13 induces tissue fibrosis by selectively stimulating and activating transforming growth factor-P 1. Journal of Experimental Medicine 2001, 194, 809-821. 

Mammalian y-aminobutyric addB receptors structure and function. Pharmacol Rev 54 247-64 Brakeman PR, Lanahan AA, O Brien R et al (1997) Homer a protein that selectively binds metabotropic glutamate receptors. Nature 386 284—8 Bremner JD, Krystal JH, Southwick SM, Chamey DS (1996) Noradrenergic mechanisms in stress and anxiety II. Preclinical studies. Synapse 23 28-38 Breysse N, Baunez C, Spooren W et al (2002) Chronic but not acute treatment with a metabotropic glutamate 5 receptor antagonist reverses the akinetic deficits in a rat model of parkinsonism. J Neurosd 22 5669-78... 

You will learn about the reaction of a-metalated phosphonic acid esters with aldehydes in Section 11.3 in connection with the Homer-Wadsworth-Emmons reaction. This reaction also seems to give a Irans-con figured oxaphosphetane (Figure 4.46). Again, a. vyn-selective /3-elim-ination of a compound with P=0 double bond should occur. One of the elimination products is (EtO)2P(=O)O0. As a second product an alkene is produced that is predominantly or exclusively irans-configured. 

Homer-Wadsworth-Emmons reactions are C=C-forming condensation reactions between the Li, Na, or K salt of a /1-koto- or an a-(alkoxycarbonyl )phosphomc acid dialkyl ester and a carbonyl compound (see Figure 4.46). These reactions furnish a,/3-unsaturated ketones or 0 ,/3-unsaturated esters, respectively, as the desired products and a phosphoric acid diester anion as a water-soluble by-product. In general, starting from aldehydes, the desired compounds are produced /ra/ov-selectively or, in the case of alkenes with trisubstituted C=C double bonds, -selectively. 

Condensations between aldehydes and metalated phosphonic acid dialkyl esters other than those mentioned previously are also referred to as Homer-Wadsworth-Emmons reactions. Nevertheless, in these esters, too, the carbanionic center carries a substituent with a pi electron withdrawing group, for example, an alkenyl group, a polyene or a C=N group. The Homer-Wadsworth-Emmons reactions of these reagents are also stereoselective and form the new C=C double bond /ra/ ,v-selectively. 

In cathodic reactions, adsorption effects would be expected to arise predominantly from adsorbed cations. Perhaps the most interesting phenomenon ascribable to adsorption of cations is the asymmetric induction observed when cathodic reduction of a prochiral substrate is performed in the presence of a chiral cation (Gourley et al., 1967 Homer and Degner, 1948). Table 18 summarizes a few selected cases of this reaction type (for reviews see Homer et al., 1972 Eberson and Homer, 1973) just to illustrate the scope of the reaction. The structural variables affecting the optical yield are unfortunately too complex to cover here. 

Brakeman PR, Lanahan AA, O Brien R, Roche K, Barnes CA, Huganir RL, Worley PF (1997) Homer a protein that selectively binds metabotropic glutamate receptors. Nature 356 284-288. 

WUtig-Horner reaction. High syn-selectivity is possible in the Wittig-Homer reaction of aldehydes with alkyl diphenylphosphonates (10, 2), formulated in equation (I). 

Z)-OL, -Unsaturated esters,l Wittig-Homer reactions generally show a preference for formation of (E)-alkenes. Thus (E)-a,p-unsaturated esters are obtained preferentially on reaction of aldehydes with trimethyl phosphonoacetate under usual conditions (potassium f-butoxide). Use of a highly dissociated base can favor (Z)-selectivity. The most effective base for this purpose is potassium hexamethyldisilazide, KN[Si(CH3)3]2, in combination with 18-crown-6, although even potassium carbonate with the crown ether is fairly effective. The (Z)-selectivity can be further enhanced by use of 1 as the phos-phonoester. Under these conditions, (Z)-unsaturated esters can be prepared from aliphatic and aromatic aldehydes with Z/E ratios as high as 50 1. The method is also useful for transformation of unsaturated aldehydes to (E,Z)-dienoates and (E,E,Z)-trienoates. 

Preparation of Derivatives. Enoate derivatives were prepared by Homer-Wittig reactions between aldehydes and the ethyl phos-phonate derived from the chloroacetyl ester of (3) in high E) selectivity (97 3). Ester derivatives were obtained by treating alcohol (3) with the corresponding carboxylic acid chloride. ... 

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