Intermolecular [4 + 2]-Cycloadditions of Nitroalkenes with Cyclic Olefins. Transformations of Cyclic Nitronates

Nitrocyclohexene undergoes facile SnCl₄-induced, [4 + 2]-cycloadditions with simple cycloalkenes to produce nitronates. The nitronates can be transformed sterospecifically into a number of other functional groups (alcohol, ketone, oxime, amine) by hydrolytic, reductive, and oxidative processes. The mechanism of the [4 + 2]-cycloaddition is believed to involve formation of a zwitterionic intermediate which can collapse via competing pathways to form the observed products. 1,3-Dipolar cycloadditions of the nitronates are described.     

[2 + 2]-Cycloadditions to Strained Bridgehead Olefins. II. Diphenylketene

The strained bridgehead olefins bicyclo [3.3.1]non-1-ene ( 1 ), bicyclo [4.2.1 ]non-1(8)-ene ( 2 ), and bicyclo [4.2.1]non-1-ene (3), and the comparable monocyclic (E)-1-methylcyclooctene ( 4 ) react with diphenylketene ( 6 ) to give a single cycloadduct 7 , 8 , 9 and 10 , respectively, in which the diphenyl-substituted C-atom is bound to the bridgehead. The structure of the cyclobutanone 8 has been determined by X-ray analysis of a twin crystal obtained by crystallization with spontaneous enrichment of enantiomers.     

[2 + 3]-Cycloadditions to C60 fullerene. Synthesis of pyrrolidinofullerenes

Pyrrolidinofullerenes were synthesized by reaction of C₆₀ fullerene with N-methylglycine and substituted aromatic aldehydes.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1695–1697.Original Russian Text Copyright © 2004 by Loginova, Gunkin.This revised version was published online in April 2005 with a corrected cover date.     

Sesquifulvalene Trapping as a [12+2] Adduct with Tetracyanoethylene

Sesquifulvalene (1) is a substance of considerable theoretical interest¹ which is expected to have a significant contribution to its structure from the dipolar resonance form 1b,² and hence an exceptionally low bond order for the central double bond. Although a wide variety of annelated and otherwise substituted sesquifulvalenes have been prepared and characterized,³ the parent substance has proved remarkably elusive. Very recently, a preparation of 1 in crystalline form has been reported, based upon elimination of an acetoxy-11,12-dihydrosesquifulvalene derivative.⁴     

Cobalt-Mediated [2 + 2 + 2]-Cycloadditions: A Maturing Synthetic Strategy [New Synthetic Methods (43)]

Dicarbonyl (η⁵-cyclopentadienyl)cobalt functions as a matrix on which a variety of unsaturated organic substrates undergo mutual bond formation. In this way α,ω-diynes cocyclize with monoalkynes to give annelated benzenes, while o-diethynylbenzenes furnish biphenylenes, and α,ω-enynes lead to the formation of complexed bi-and tricyclic dienes. Nitriles cocyclize with two alkynyl groups to give pyridines and other heterocycles, isocyanates allow access to annelated 2-pyridones, and incorporation of carbon monoxide provides complexed cyclopentadienones. In many cases remarkable chemo-, regio-, and stereoselectivity are observed, partially facilitated by use of the trimethylsilyl substituent as a controlling group. The scope and level of maturity of the method are demonstrated by the synthesis of a series of hitherto inaccessible, novel, and theoretically interesting molecules, and by its utilization in several unique approaches to a variety of natural products, e.g. protoberberines, steroids, vitamin B₆, and camptothecin.