Naphthols - the DOtz reaction

The DOtz reaction was traditionally carried out in ethereal solvents for many years more recently solvents of low coordinating ability have been found to be superior in most situations, with yields in excess of 80 7o available from annulation of simple alkynes to arylcarbenes in hexane [13]. In fact, it has become increasingly clear that manipulation of reaction conditions, including solvent, temperature, and concentration, can be used in a synthetically useful way to drastically alter product distributions (see Sections 5.2.2 and 5.2.3). Additionally, dry-state adsorption techniques, which have expanded the utility of the Pauson-Khand reaction (see Section 5.3.3), show promise for increased reaction rates and yields in the D6tz reaction [14]. 

Annulation can take place with virtually any rt-system attached to a carbene C-atom, including a variety of aromatic, heteroaromatic, and simple vinyl systems [Eqs. (2)-(4)] [15]. 

Replacing the oxygen atom of the Fischer carbene with other heteroatoms provides a valuable variation. Arylaminocarbenes show a marked chemoselectivity for producing the indane nucleus, which is attributed to the stronger donor character of the amino group relative 

The intramolecular DOtz reaction, in which the alkyne is tethered to the carbene, improves synthetic efficiency and regiocontrol, although internal alkynes work better than terminal alkynes [30], Such cycloadditions provided the kqr to a synthesis of the antibiotic deoxy-frenolicin [Eq. (12)] [31] and played a role in work aimed toward the synthesis of the ben-zofuran angelicin, in which a 3-furylcarbene complex aimulates toward C2 of the furan, avoiding forming an isobenzofuran structure [Eq. (13)] [32]. 

Reaction efficiency can also be enhanced by the use of tandem reactions, one-pot combinations of the Dotz reaction with other ring-forming reactions, including Diels-Alder, and nucleophilic aromatic addition reactions [33]. For example, alkynyl groups attached to Fischer 

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The first carbene compound to be well characterized was prepared in 1966 and was one of many Fischer-Type Carbene Complexes to be reported (see equation 7). Fischer carbenes are characterized by heteroatom substituents at the carbene carbon, stabilization by a low-valent metal center, and a partial positive charge at the carbene carbon. In contrast, Schrock-Type Carbene Complexes, or alkylidenes," that have alkyl substituents, are found on metal centers in higher oxidation states, and are nucleophihc at carbon. Many Fischer carbenes are known for chromium, whereas chromium alkylidenes are much less common. Monohalocarbenes of chromium, for example, (OC)5Cr=C(F)NEt2, have also been extensively investigated." Two carbene reactions of note for their application to organic synthesis are the cycloaddition of alkenes with carbene complexes and the reaction of aromatic carbenes with aUcynes to yield complexed naphthols (the Dotz reaction ). ... 

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