Pt-Catalyzed Rearrangement of Oxaspirohexanes to 3-Methylenetetrahydrofurans: Scope and Mechanism

Abstract

A novel Pt-catalyzed rearrangement of oxaspirohexanes to 3-methylenetetrahydrofurans is reported. Mechanistic studies by (13)C-labeling experiments confirm oxidative addition of Pt(II) regioselectively to the least substituted carbon-carbon bond of the cyclopropane to form a platinacyclobutane intermediate. To our knowledge, this is the first alkoxy-substituted platinacyclobutane that has been observed spectroscopically. The scope and a proposed mechanism of this new Pt-catalyzed transformation are described.

Oxetanes: Recent Advances in Synthesis, Reactivity, and Medicinal Chemistry

“…Oxaspirohexanes that were synthesized from 2-methyleneoxetanes also underwent rearrangement catalyzed by Zeise's Pt(II) dimer. 483 Monosubstituted as well as 5,6-transdisubstituted oxaspirohexanes rearranged in good yields via a platinacyclobutane intermediate (Scheme 130). 5,6-cis-disubstituted oxaspirohexanes ring-opened to afford allyl chlorides as the major product.…”

Oxetanes and Oxetenes: Fused-Ring Derivatives

“…<Scheme 31 near here> Spirocyclopropyl oxetanes 121 were reported to rearrange to 3-methylenetetrahydrofurans 122 upon treatment with a catalytic amount of Zeise's dimer and 20 mol% of tricyclohexylphosphine in dichloromethane at 45 °C. 102 The mechanism of this new platinum-catalyzed rearrangement was extensively studied (including with 13 C NMR-labeling) and it was found that oxidative addition of the substrate to platinum(II) was taking place at the least substituted carbon-carbon bond of the spirocyclopropyl unit. <Scheme 32 near here> Spirocyclic oxetanes 123, obtained by photocycloaddition of N-acylisatins and bicyclopropylidene, could be ring-opened by an excess of acid, such as hydrochloric or hydrobromic acid in acetonitrile at room temperature, yielding spirocyclopropyl butenolide 124 in good yield.…”

Stereoselective Aldol Additions of Glycolic Acid and Its Derivatives

“…an analogue containing S-tert-butyl (R 1 = t-Bu) rather than S-phenyl adds to other aldehydes with even greater antiselectivity ( Table 10). [85][86][87][88] Replacing O α -benzylglycolic acid S-phenyl thioester (80, R 1 = Ph, see Table 10) by O α -(tert-butyldimethylsilyl)glycolic acid S-phenyl thioester (82) as a CH acid results in Cl 3 Ti enolate formation and aldol additions that furnish the aldol adducts syn-83 with ds = 72:28 to 90:10 (Table 11). 85 Enantiomerically pure (homoisomenthyl) 2 B enolates derived from the last-mentioned S-phenyl thioester of O α -(tert-butyldimethylsilyl)glycolic acid (84, R 1 = Ph, PG = SiMe 2 t-Bu) or derived from the S-phenyl or S-tert-butyl thioester of a differently protected O α -benzylglycolic acid (84, R 1 = Ph or t-Bu, PG = Bn) undergo aldol additions with excellent asymmetric inductions and anti-selectivities (Table 12).…”