Regulation of Diastereoselectivity in the Carbocyclization of Allenyl (<i>S</i>)‑<i>N</i>-<i>tert</i>-Butylsulfinimines through a Three-Component Assembly

Allenyl sulfinimines can be stereoselectively cyclized with hexamethylditin under palladium catalysis conditions followed by a selection of additives for an activated transmetalation. Reactivity and diastereoselectivity for the cyclization strongly depend on the characteristics of additives. A highly diastereoselective synthesis of five-membered rings is achieved from the reaction of the corresponding allenyl (<i>S</i>)-N-<i>tert</i>-butylsulfinimies through the following sequence. After the distannylation of the allenyl group with hexamethylditin catalyzed by the Pd complex, stereochemical routes are additive dependent: addition of SnCl₄ affords a <i>cis</i> ring exclusively, whereas a <i>trans</i> ring is formed predominantly by the introduction of <i>B</i>-bromocatecholborane. Extension of the methodology to the synthesis of six-membered <i>cis</i> rings is achieved by using <i>B</i>-bromocatecholborane. Stereochemical relationships of products were unambiguously deduced by X-ray crystallography

Unexpected Skeletal Rearrangement in the Gold(I)/Silver(I)-Catalyzed Conversion of 7‑Aryl-1,6-enynes to Bicyclo[3.2.0]hept-6-enes via Hidden Brønsted Acid Catalysis

Cycloaddition of an isotopically labeled 7-phenyl-1,6-enyne catalyzed by a mixture of LAuCl [L = P­(<i>t</i>-Bu)₂<i>o</i>-biphenyl)] and AgSbF₆ forms the corresponding 6-phenylbicyclo[3.2.0]­hept-6-ene with concomitant scrambling of the olefinic CPh (C6) and CH (C7) groups of the product. The extent of C6/C7 scrambling was sensitive to the nature of the silver salt and was likewise observed in the cycloaddition of the 7-phenyl-1,6-enyne catalyzed by mixtures of [LAuNCMe]⁺SbF₆^– and Brønsted acids such as HOTf. These observations and low-temperature NMR analysis of organic and organometallic intermediates in the cycloaddition process were in accord with a mechanism for C6/C7 scrambling initiated by protonation of free bicyclo[3.2.0]­hept-7-ene to generate a bicyclo[3.2.0]­heptyl cation that undergoes reversible alkyl migration, presumably involving bicyclo[4.1.0]- and bicyclo[3.1.1]­heptyl cations prior to elimination of the C7 proton