Benzoic acids, oxidative annulations with

The 6-endo activated epoxy alcohol cyclization process was also expected to play a central role in the annulation of pyran ring G of the natural product (see Scheme 22). Silylation of the free secondary hydroxyl group in compound 131 furnishes, after hydrobora-tion/oxidation of the double bond, compound 132. Swern oxidation of alcohol 132 produces an aldehyde which reacts efficiently with (ethoxycarbonylethylidene)triphenylphosphorane in the presence of a catalytic amount of benzoic acid in benzene at 50 °C, furnishing... 

Ruthenium(II)-mediated oxidative annulation reaction of benzoic acids and cyclopropylarylethynes furnishes a mixture of 3- and 4-cyclopropyl substituted isocoumarins (130BC142).A facile one-pot synthesis of4-aryl-isocoumarins involves an acidic hydrolysis of ( -2-(l-aryl-2-methoxy-ethenyl)benzaldehydes with HBr and subsequent oxidation with PCC (13HCA2173). 

Reactions with alkynes may lead to the formation of cyclized products. The reaction of iodobenzenes with two equivalents of an alkyne has been shown to give naphthalene derivatives in the presence of cobalt catalyst with a manganese reduc-tant. The process, shown in Scheme 15, is thought to involve oxidative addition of the aryliodide to cobalt followed by double alkyne insertion. The cobalt-catalysed annulation step probably involves an pathway. The cyclopentadienyl-rhodium-catalysed annulation of benzoic acids with alkynes has been used to form isocoumarin derivatives, such as (126). The process is thought to involve cyclorhodation at the ortho-position of a rhodium benzoate intermediate, followed by alkyne insertion to form a seven-membered rhodacycle and reductive elimination The silver-catalysed annulations of diphenylphosphine oxides with alkynes proceed in the absence of rhodium. Benzophosphole oxides such as (127), formed with diphenylethyne, are produced. Here, the proposed mechanism involves homolytic cleavage of the phosphorus-hydrogen bond to give a radical which can add to the alkyne and subsequently cyclize. ... 

The first example of Rh(III)-catalyzed oxidative carbonylation of aromatic amides by C-H/N-H activation to synthesize phthalimides, such as 42, was reported by Rovis in 2011 [26a]. The presence of KH2PO is crucial to obtain the products in high yields (Eq. (5.41)). This reaction tolerates a variety of functional groups under standard conditions to afford phthalimides in excellent yields. Similarly, a Rh(III)-catalyzed direct C-H amidation of benzoic acids with isocyanates and subsequent intramolecular cyclization to give Af-substituted phthalimides, such as 43, is also known. This cascade cyclization reaction provided various phthalimides in 26-91% yield [26b]. In this case, NaOAc plays a vital role for the annulation and stimulation of the ortho-C-H bond activation of the benzoic acids (Eq. (5.42)). 

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