Nickel-Catalyzed Regio- and Stereoselective Reductive Coupling between Methylenecyclopropanes, Aldehydes, and Triethylborane with Retention of the Cyclopropane Ring
Running rings: The first regio‐ and stereoselective reductive coupling between methylenecyclopropanes, aldehydes, and triethylborane with retention of the cyclopropanering was achieved using a nickel–phosphine catalyst (see scheme). The reductive coupling reaction constructed a stereo‐defined cyclopropanering with formation of a quaternary stereogenic carbon center.
Preparation of both enantiomers of a synthon for novel nucleoside analogs by enzymatic desymmetrization of a meso-diol with a methylene cyclopropane skeleton
The enzymaticdesymmetrization of methylenecyclopropane diol or its corresponding diacetate derivative, generated from a [2+1] cycloaddition between dioxepin and methylchlorocarbene, is described. After screening five commercial lipases, the two enantiomers of acetic acid 2-hydroxymethyl-3-methylene-cyclopropylmethyl ester are obtained in high yields and excellent enantioselectivities by using PFL
Reactions of co-ordinated ligands. Part XIII. Ring opening of 2,3-bis-(hydroxymethyl)methylenecyclopropane with nonacarbonyldi-iron: molecular and crystal structures of tricarbonyl-η<sup>4</sup>-[3-methylene-endo-4-vinyldihydrofuran-2(3H)-one]iron(<scp>0</scp>) and tetracarbonyl-η<sup>2</sup>-[3-methyl-ene-exo-4-vinyldihydrofuran-2(3H)-one]iron(<scp>0</scp>)
作者:Barbara M. Chisnall、Michael Green、Russell P. Hughes、Alan J. Welch
DOI:10.1039/dt9760001899
日期:——
trans- or cis-2,3-Bis(hydroxymethyl)methylenecyclopropanes react with [Fe2(CO)9] to produce tricarbonyl-η4-[3-methylene-endo-4-vinyldihydrofuran-2(3H)-one]iron(0) and tetracarbonyl-η2-[3-methylene-exo-4-vinyldihydro-furan-2(3H)-one]iron(0). The structural identities of these two complexes have been established by the analysis of single-crystal X-ray data recorded on a four-circle diffractometer.
Synthesis of (Z)-(2,3-bis-hydroxymethyl)methylenecyclopropane analogues of nucleosides adenosine 10a, 10b, 10c and 17 is described. Epimerization of Feist's acid (11) using acetic anhydride gave cyclic anhydride 12 which was reduced in situ to give diol 13. Acetylation (compound 14) followed by addition of bromine led to dibromo derivative 15. Alkylation-elimination of adenine with 15 afforded, after deacetylation, analogue 10a. Similar treatment of 2-amino-6-chloropurine and 2,6-diaminopurine led to diacetates 16 and 18. Deprotection then gave compounds 17 and 10c. Hydrolysis of 17 furnished guanine analogue 10b. Compounds 10a, l0b or 10c were inactive against HCMV, HSV-1, HSV-2, EBV, VZV and HBV. Analogues 10a and 10b were also assayed for anti-HIV activity. Compound 10a was effective in HIV-1/MT-2 culture with EC50/CC50 33/> 100 muM but 10b was inactive. Analogue 10a was not a substrate for adenosine deaminase.
Enhanced Catalyst Activity and Enantioselectivity with Chirality-Switchable Polymer Ligand PQXphos in Pd-Catalyzed Asymmetric Silaborative Cleavage of <i>meso</i>-Methylenecyclopropanes
The poly(quinoxaline-2,3-diyl)-based helically chiral phosphine ligands PQXphos exhibited high enantioselectivities up to 97% ee in palladium-catalyzed desymmetrization of meso-1,2-dialkylsubstituted-3-methylenecyclopropanes through silaborative cleavage of the C C bond. The observed enantioselectivities were higher than those obtained with 2-diarylphosphino-1,1'-binaphthyl in our original report. Remarkable rate enhancement was also observed with a series of PQXphos in comparison with the corresponding low-molecular weight ligands.