Petasis reagent

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 212, Springer International Publishing Switzerland 2014 

Petasis N A. Bzowej, E. I. J. Am. Chem. Soc. 1990, 112, 6392-6394. Nicos A. Petasis is a professor at the University of Southern California in Los Angeles. 

Naskar, D. Neogi, S. Roy, A. Mandal, A. B. Tetrahedron Lett. 2008, 49,6762-6764. Zhang, J. Tebbe Reagent. In Name Reactions for Homologations-Part I, Li, J. J. Ed., Wiley Hoboken, NJ, 2009, pp 319-333. (Review). 

Alkenes firom a-silyl caibanions and caibonyl compounds. Also known as the sila-Wittig reaction. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 198, Springer-Verlag Berlin Heidelberg 2009 

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Both the Tebbe and Petasis reagents, Cp2CH2ClAlMe2 and Cp2TiMe2, effect the direct conversion of alkenic esters to dihydropyrans. This olefin metathesis has been successfully applied to the synthesis of complex polyether frameworks <96JA1565,96JA10335>. 

Scheme 6.77 (a) Methylenation of ketones with the Petasis reagent,... 

Keywords Ring-closing metathesis, Epothilones, Tebbe reagent, Petasis reagent, Maitotoxin... 

A limitation to the use of the Tebbe reagent 93 was observed during the attempted conversion of substrates 139 and 142 to the tricyclic systems 141 and 144 respectively (Scheme 21). The major products from these reactions were olefinic alcohols 140 and 143. These products presumably resulted from sequential hydrolysis and olefination of the initially formed cyclic enol ethers. The problem associated with these sensitive substrates was overcome through use of the less Lewis-acidic Petasis reagent 110, which provided access to the desired products 141 and 144 [34a]. 

Scheme 21. Titanium-mediated metathesis strategy for the synthesis of cyclic enol ethers and hydroxy olefins, (a) Tebbe reagent (93), THF, reflux, 41% (140), 41% (143) (b) Petasis reagent (110), THF, reflux, 60% (141), 30% (144) (Nicolaou et al.) [34a]...

Dimethyltitanocene (213), called the Petasis reagent, can be used for alkenation of carbonyls (aldehydes, ketones, esters, thioesters and lactones). This reagent is prepared more easily than the Tebbe reagent by the reaction of titanocene dichloride with MeLi. However, this reagent may not be a carbene complex and its reaction may be explained as a nucleophilic attack of the methyl group at the carbonyl [67], Alkenylsilanes are prepared from carbonyl compounds. Tri(trimethylsilyl)titanacyclobutene (216), as a... 

Scheme 3. Carbonyl methylenation with the titanium-methylene species 4 prepared from the Tebbe, Grubbs, or Petasis reagents (1 - 3).

Tebbe reagent, Grubbs reagent, Petasis reagent, Takeda reagent and Takai reagent are... 

The Petasis reagent, dimethyl titanocene (4.93) can also be used for the methylenation of carbonyl compounds. The Petasis reagent (4.93) is prepared by the reaction of methyl magnesium chloride or methyllithium with titanocene dichloride (Cp2TiCl2). Carbonyl compounds on heating with 4.93 at 60-65° C in a toluene solution give the corresponding alkenes or enol ethers. 

A useful alternative to phosphorus ylids are the titanium reagents, such as, 71, prepared from dicyclopentadienyltitanium dichloride and trimethylaluminum. Treatment of a carbonyl compound with the titanium cyclopentadienide complex 71 Tebbe s reagent) in toluene-THF containing a small amount of pyridine " leads to the alkene. Dimethyltitanocene (Me2TiCp2), called the Petasis reagent, is a convenient and highly useful alternative to The mechanism of Petasis... 

Besides stability and ease of preparation, another advantage of the Petasis reagent is that stmctural analogs can be prepared, including Cp2Ti(C3H5)2... 

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