Formal [3+3]- and [3+2]-cycloadditions of allylsilanes with benzylic cations

Chiral Benzylic Carbocations: Low-Temperature NMR Studies and Theoretical Calculations

“…The first 13 C NMR spectrum of such a cation was obtained in 1971 . Benzylic cations have been invoked as intermediates in many reactions, including Friedel−Crafts alkylation reactions, [3 + 2]-cycloaddition reactions, and rearrangements . Possibly because of their high reactivity, chiral benzylic cations have not been extensively studied as intermediates in diastereoselective C−C bond formation reactions.…”

Synthesis of Substituted Piperidines from N,N-Bis[(benzotriazol-1-yl)methyl]amines

“…[3 + 3] cycloaddition reactions are of considerable importance and utility in the syntheses of six-membered heterocyclic systems. 10a-d Most such reactions involve the condensation of a 1,3-dinucleophile (e.g. amidine, guanidine, urea, thiourea, or sulfamide) with a 1,3-dielectrophile (e.g., 1,3-dicarbonyl compound, related species such as cyanoacetic esters and malononitriles, or α,β-unsaturated aldehydes, ketones, esters, and nitriles).…”

The synthesis of carbocyclic aromatic systems

“…'6 Dihydrophthalate esters, or dihydrophthalic acids, prepared by the electrochemical reduction of phthalates or phthalic acids, react with alkynes such as DMAD to yield a range of I ,2-disubstituted arenes and biaryl systems, with the elimination of dimethyl fumarate or fumaric acid (Scheme 4).x7 Loss of sulfur dioxide has been used as a means of aromatising [4+2] cycloadducts, for example in the conversion of 115 to 116 and 117;" a recent report describes the cycloadditions of thienopyrrole dioxides." The conversion of 115 to 116 also involves loss of one mole of benzenesulfinic acid.108; p reactions by loss of pyrrolidine and morpholine,""3 and by addition of ally1 silanes to benzyl cations 94. A more complex loss still is involved in the conversion of 118 to 123.…”