Electrophilic halogenations of propargyl alcohols: paths to α-haloenones, β-haloenones and mixed β,β-dihaloenones.

The Meyer-Schuster rearrangement of propargyl alcohols or alkynols leading to α,β-unsaturated carbonyl compounds is well known. Yet, electrophilic halogenations of the same alkynols and their alkoxy, ester and halo derivatives are inconspicuous. This review on the halogenation reactions of propargyl alcohols and derivatives intends to give a perspective from its humble direct halogenation beginning to the present involving metal catalysis.

Halogen bond-induced electrophilic aromatic halogenations.

In recent years, there has been increasing interest in utilising halogen bonds in organic synthesis, especially in aromatic halogenation reactions. -Halosuccinimides and 1,3-dihalo-5,5-dimethylhydantoins are popular sources of halonium ions due to their ease of handling and low toxicities. Traditionally, these -haloimides are activated by electrophiles, namely Brønsted and Lewis acids.

Halogen bonding in (Z)-2-iodocinnamaldehyde.

Based on the bulkiness of the iodine atom, a non-planar conformation was expected for the title compound. Instead, its molecular structure is planar, as experimentally determined using single crystal X-ray diffraction, and confirmed theoretically by DFT calculations on the single molecule and the halogen pair paired molecules, therefore ruling out crystal packing forces as a principal factor leading to planarity. Indeed, planarity is ascribed to the carbonyl double bond, as when this bond is saturated on forming the related alcohol derivative, the molecule loses planarity.

N-Acetyl-3,5-dibromo-l-tyrosine hemihydrate.

The title compound, C(11)H(11)Br(2)NO(4)·0.5H(2)O, was prepared by an electrophilic bromination of N-acetyl-l-tyrosine in acetonitrile at room temperature. The two independent mol-ecules do not differ substanti-ally and a mol-ecule of water completes the asymmetric unit.

Novel Photochemical Hydrolysis of o-Acetylphenylacetonitriles to Amides.

Irradiation of o-acetylphenylacetonitriles 1a,b in methanol (lambda >280 nm) leads to essentially quantitative photohydrolysis with formation of the corresponding ketal amides 3a,b. The mechanism proposed for this novel reaction is supported by the qualitatively different photochemical behavior of 1c and by a labeling experiment with 1a-L that confirms transfer of the carbonyl oxygen atom of 1a to the amide oxygen atom of 3a.