NHC-Catalyzed Formal [2+2] Annulations of Allenoates for the Synthesis of Substituted Oxetanes.

An N-heterocyclic carbene (NHC)-catalyzed reaction of γ-substituted allenoates for the synthesis of substituted oxetanes has been developed. The method provides an approach to access substituted oxetanes in a single step and is the first example of an NHC-catalyzed formal [2+2]-annulation employing γ-substituted allenoates with trifluoromethyl ketones. Mechanistic and modeling studies provide a rationale for the divergence in reactivity observed compared to the analogous reaction using unsubstituted allenoates and inform a hypothesis to explain the observed diastereoselectivity under different reaction conditions.

Catalytic Asymmetric Transfer Hydrogenation of trans-Chalcone Derivatives Using BINOL-derived Boro-phosphates.

Chiral phosphoric-acid-catalyzed asymmetric reductions of trans-chalcones have been investigated in this work. A BINOL-derived boro-phosphate-catalyzed asymmetric transfer hydrogenation of the carbon-carbon double bond of trans-chalcone derivatives employing borane as a hydride source was realized. This methodology provides a convenient procedure to access chiral dihydrochalone derivatives in high yields and with high enantioselectivities under mild conditions.

Convenient method for preparing benzyl ethers and esters using 2-benzyloxypyridine.

2-Benzyloxy-1-methylpyridinium triflate (1) is emerging as a mild, convenient, and in some cases uniquely effective new reagent for the synthesis of benzyl ethers and esters. This article provides a revised benzyl transfer protocol in which N-methylation of 2-benzyloxypyridine delivers the active reagent in situ. Observations on the appropriate choice of solvent (toluene vs. trifluorotoluene) and the extension of this methodology to the synthesis of other arylmethyl ethers are included.