No abstract

No abstract

A facile method for preparing the 2H-benz[cd]azulene system, based upon an elaboration of the guaiazulene framework, is presented. Aerial oxidation to the corresponding 8-(2-propylidene)-benz[cd]azulene, and also cycloaddition reactions with tetracyanoethylene (TCNE), are described. The first X-ray crystal structure of a 2H-benz[cd]azulene, as an eta6-coordinated Cr(CO)3 complex, is reported.

In an endeavor to utilize metal carbonyl complexes of acetylenic aldehydes and ketones to control the stereoselectivity of nucleophilic acyl addition, the dicobalt hexacarbonyl and dicobalt pentacarbonyl(triphenylphosphine) complexes of 3-phenylpropynal and 2-hexynal were conveniently prepared. Crotyl transfer from either (E)-or (Z)-crotyltributylstannane to Co 2 (CO) 6 -complexed 3-phenylpropynal and 2-hexynal produced 3,4-disubstituted-1,5enynes with high syn diastereoselectivity. Allyl and 2-methylallyl transfer to Co 2 (CO) 5 PPh 3complexed aldehydes was also accomplished with high yields and diastereoselectivities. In all cases, decomplexation of the metal carbonyl moiety was effected, selectively, under very mild oxidative conditions. Exchange of a CO by PPh 3 led to decreased overall reactivity. Two competing kinetic processes were observed: stereoselective allylation was observed at low temperature, but at higher temperatures, the first formed allylic alcohol preferentially underwent elimination leading to dienynes.

No abstract

The Sisyl (tris(Trimethylsilyl)silyl) Group: A Fluoride Resistant, Photolabile Alcohol Protecting Group.-Various primary and secondary alcohols are protected as tris(trimethylsilyl) ethers (III), stable to organometallic, oxidation, and selected fluoride reagents as well as under acidic conditions. Deprotection of the silyl ethers is achieved by irradiation or in the presence of tetrabutylammonium fluoride.-(BROOK, M. A.; GOTTARDO, C.; BALDUZZI, S.; MOHAMED, M.; Tetrahedron Lett. 38 (1997) 40, 6997-7000; Dep. Chem., McMaster Univ., Hamilton, Ont. L8S 4M1, Can.; EN)

The Photolytic and Hydrolytic Lability of Sisyl (Si(SiMe 3 ) 3 ) Ethers, an Alcohol Protecting Group.-A detailed account of recently published studies on the scope of the sisyl protection group is presented. Sisyl ethers are found to be stable to less reactive organometallic compounds, phosphorylides, oxidation, and selected fluoride salts. Reaction with BuLi or LiAlH 4 furnishes mixtures of deprotection and decomposition compounds. Clean deprotection is achieved by photolysis or using TBAF. Relative rates for acidic hydrolysis are determined. Following orders for the ease of hydrolysis are observed: RO-Si(Tms) 3 ¿ RO-Tbs (aq. AcOH) and RO-Tbs ¿ RO-Si(Tms) 3