Shapiro coupling

The allylalkohol 6 turns out to be the obvious precursor of the protected diol 5, and 6 reasonably arises from a Shapiro coupling of cyclohexadienyllithium 7 with the cyclohexene-4-aldehyde 8 which is the product of oxidation and subsequent diol protection of the bicyclic hydroxylactone 9 the latter emerges from rearrangement of the Diels-Alder cycloadduct 13 of 3-hydroxy-2-pyrone 14 as the diene and 4-hydroxy-2-methyl-2-butenoate 15 as the electron-deficient dienophile. The cyclohexadienyllithium 7 originates from the sulfonylhydrazone of the ketone 10 which is, once again, a Diels-Alder cycloadduct of the protected 3-hydroxymethyl-2,4-dimethyl-l,3-pentadiene 12 and ketene 11 as the dienophile. 

Shapiro coupling of cyclohexadienyllithium 7, prepared by reacting the sulfonyl-hydrazone 18 with butyllithium in THF, with the cyclohexenaldehyde 8, leads exclusively to the desired stereoisomer 6. The unexpected selectivity probably arises from steric overcrowding of the Si face of the prochiral chelated aldehyde carbonyl in 8 thus enabling the nucleophilic alkenyllithium to approach predominantly from the less-hindered Re face. 

A special application of the Japp-Klingemann/Eischer sequence is in the preparation of tryptamines from piperidone-3-carboxylate salts, a method which was originally developed by Abramovitch and Shapiro[2]. When the piperidone is subjected to Japp-Klingemann coupling under mildly alkaline conditions decarboxylation occurs and a 3-hydrazonopiperidin-2-one is isolated. Fischer cyclization then gives 1-oxotetrahydro-p-carbolines which can be hydrolysed and decarboxylated to afford the desired tryptamine. 

Liebeskind and associates converted 3,4-diisopropyl squarate (97) to stannylcyclobutenedione 98 via a 1,4-addition-elimination sequence. 98 was then coupled with 2-iodothiophene to afford substituted cyclobutenedione 99 [85]. In another case, 3-lithioquinuclidin-2-ene, generated from the Shapiro reaction of 3-quinuclidinone (100), was quenched with Bu3SnCl to afford a unique enamine stannane 101. The Stille reaction of stannane 101 and 5-bromo-2-formyl-thiophene then furnished 3-thienylquinuclidine 102 [86]. 

Shapiro s data for formaldehyde (Table 16) are quite limited, but clearly show a solvent induced decrease for VH D (which is multiplied by the ratio of the gyromagnetic constants of H and D to yield the H—H coupling) going from TMS to acetonitrile. 

Conjugated dienes can be prepared from certain ketones via their trisylhydrazones (386) by the Shapiro reaction (equation 102). This involves a reductive metallation to a vinyllithium intermediate, transmetallation, for example, with Cu(I) iodide, and oxidative coupling. ... 

Shapiro DJ, Rodwell VW 1969 Diurnal variation and cholesterol regulation of hepatic HMG-CoA reductase activity. Biochem Biophys Res Commun 37 867—872 Silver R, LeSauter J, Tresco PA, Lehman MN 1996 A diffusible coupling signal from the transplanted suprachiasmatic nucleus controlling circadian locomotor rhythms. Nature 382 810-813... 

In particular, Shapiro and others calculated state-to-state photodissociation cross sections from vibrationally excited states of HCN and DCN [58], N2O [59], and O3 [60]. Eor instance, the detailed product-vibrational state distributions and absorption spectra of HCN(DCN) were compared [58]. These results were obtained employing a half-collision approximation, where the photodissociation could be depicted as consisting of two steps, that is, absorption of the photon and the dissociation, as well as an exact numerical integration of the coupled equations. In particular, it was predicted that large isotope effects can be obtained in certain regions of the spectrum by photodissociation of vibrationally excited molecules. 

The Cqq, are generalized centrifugal potentials which are proportional to R 2 the proportionality constants depend on J,p,j, and Q, and they are explicitly given by Balint-Kurti and Shapiro (1981). The wavenumbers kj are defined in (3.21) and the potential coupling elements are given by... 

The theory outlined above can be used to calculate the exact bound-state energies and wavefunctions for any triatomic molecule and for any value J of the total angular momentum quantum number. We can solve the set of coupled equations (11.7) subject to the boundary conditions Xjfi (R Jp) —> 0 in the limits R —> 0 and R — oo (Shapiro and Balint-Kurti 1979). Alternatively we may expand the radial wavefunctions in a suitable set of one-dimensional oscillator wavefunctions ipm(R),... 

It is not difficult to surmise that the final expression for the fully resolved differential photodissociation cross section is extremely complicated (Balint-Kurti and Shapiro 1981). It contains vast quantities of sums and angular momentum coupling elements. Note that the cross section depends explicitly on the magnetic quantum numbers Mi and mj. Somewhat simpler cross section expressions can be derived by averaging over the initial projection quantum number Mi and summing over the final projection quantum number of the rotor, mj. As shown by Balint-Kurti and Shapiro, the angle-resolved cross section then takes on the general form... 

Because it is computationally more convenient, most researchers choose the diabatic rather than the adiabatic representation if they try to fit experimental data. In addition to the two diagonal elements of the potential matrix, and V22 5 one merely needs a third potential (surface) which provides the coupling between the diabatic states (Shapiro 1986 Guo and Schatz 1990a,b Dixon, Marston, and Balint-Kurti 1990). 

It is well established that activation of G protein-coupled receptors (GPCRs), in particular those that couple to the Got / subunit, can result in potent inhibition of both N-type and P/Q-type calcium channels (Figure 2) (Beech et al. 1992 Bemheim et al. 1991 Caulfield et al. 1994 Dunlap and Fischbach 1981 Golardand Siegelbaum 1993 Ikeda 1992 Ikeda and Schofield 1989 Lipscombe et al. 1989 Mintz and Bean 1993 Shapiro and Hille 1993 Zhu and Ikeda 1993). The physio-... 

R. R. Alfano, S. L. Shapiro, Emission in the region fOOO to 7000 A via four-photon coupling in glass, Physical Review Letters 24, 584 (1970)... 

Light J.C. and Walker. E.B. (1976) An B matrix approach to the solution of coupled equations for atom-molecule reactive scattering, J. Chem. Phys. 65. 4272-4282. Halavee, U. and Shapiro, M. (1976) A collinear analytic model for atom-diatom chemical reactions, J. Chem. Phys. 64, 2826-2839. 

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