Conjugate Addition of a Silyl Ketene Acetal to α,β‐Unsaturated Lactones

Abstract

Conjugate addition of a silyl ketene acetal [Me₂C?C (OMe)OSiMe₃] to α,β‐unsaturated lactones (namely, 5,6‐dihydro‐2H‐pyran‐2‐one, 2(5H)‐furanone as Michael acceptor) occurs efficiently at room temperature in the presence of a nucleophilic catalyst, tetra‐n‐butyl ammonium bibenzoate (TBABB), in THF as well as Lewis acid catalysts such as Yb(OTf)₃ and I₂ in CH₂Cl₂, giving the corresponding 1,4‐adducts in excellent yields.     

Nickel‐Catalyzed Cross‐Electrophile Coupling of Aryl Bromides with Pyrimidin‐2‐yl Tosylates

A new protocol for the NiCl₂ ‐catalyzed cross‐electrophile coupling of aryl bromides with pyrimidin‐2‐yl tosylates to give the corresponding C2 ‐arylation pyrimidine derivatives has been developed. This study provides an improvement over previous methods by using pyrimidin‐2‐yl tosylates instead of halides as coupling partners that are stable and easily available.     

Perfluorovinyl Morpholine and Perfluorovinyl Pyrrolidine with Nucleophiles and Electrophiles

In this study, both monofunctional and bifunctional nucleophiles, as well as the electrophile FNO, are reacted with perfluorovinyl amines. The perfluorovinyl amines CF?CF₂ and CF?CF₂ have been reacted with dimethylamine and diethylamine in the presence of small amounts of water to give CHFC(O)N(CH₃)₂ ( 1 ), CHFC(O)N(CH₃)₂ ( 2 ), and CHFC(O)N(C₂H₅)₂ ( 3 ). With perfluorovinyl pyrrolidine and perfluorovinyl morpholine, ethanolamine gives the cyclized products CHF ( 4 ) and CHF ( 5 ), respectively. Reaction of the vinyl amines with (CH₃)₃SiOCH₂CF₃ in the presence of catalytic amounts of CsF results in the formation of cis- ( 6 ) and trans- ( 7 ) CF?CF(OCH₂CF₃) and cis- ( 8 ) and trans- ( 9 ) CF?CF(OCH₂CF₃). The electrophile FNO reacts slowly with perfluorovinyl pyrrolidine and perfluorovinyl morpholine, and more rapidly with (CF₃)₃CCF?CF₂ to give CF(NO)CF₃ ( 10 ), CF(NO)CF₃ ( 11 ) and (CF₃)₃CF(NO)CF₃ ( 12 ), respectively. Single crystal X-ray analysis is used to confirm the identity of the product obtained from the controlled hydrolysis of the sultone of perfluorovinyl pyrrolidine as the sulfonic acid anhydride C(O)CF₂OS(O)₂OCF₂C(O) ( 13 ). The X-ray crystal structure of perfluorosuccinic acid monohydrate ( 14 ), which is obtained when the perfluorovinyl pyrrolidine sultone is hydrolyzed in excess water, is also reported for the first time.     

Divergent cyclisations of 2-(5-amino-4-carbamoyl-1H-pyrazol-3-yl)acetic acids with formyl and acetyl electrophiles

The reaction of 2-(5-amino-4-carbamoyl-1-methyl-1H-pyrazol-3-yl)acetic acid and triethylorthoformate did not give the expected dihydropyrazolo[4,3-c]pyridin-4-one product as described in literature, but formed an alternative cyclic imide product, fully characterised by NMR and X-ray crystallography. This mode of reaction was shown to be general to other 1-substituted-2-(5-amino-4-carbamoyl-1H-pyrazol-3-yl)acetic acids. The outcome of the cyclisation was highly sensitive both to the nature of the reagents used and also to the acidity of the reaction medium, such that a number of interesting bicyclic heterocycles could be produced in a controlled fashion from the single starting material. The major tautomeric forms of the bicyclic products in solution were found to vary according to their substitution pattern.     

Synthesis of New (Pyrimido[4,5-e][1,3,4] thiadiazin-7-yl)hydrazine Derivatives

New (pyrimido[4,5-e][1,3,4]thiadiazin-7-yl)hydrazines were synthesized via the cyclocondensation of alkyl-2-phenylhydrazinecarbodithioates as bidentate nucleophiles with 5-bromo-2,4-dichloro-6-methylpyrimidine as an electrophile and further replacement of chlorine atom on the seven number position of pyrimido[4,5-e][1,3,4]thiadiazin by hydrazine in boiling ethanol.     

Fast Synthesis of Benzofluorenes by Selenium‐Mediated Carbocyclizations

When one ring is not enough : A new double cyclization of stilbene derivatives results in benzo[b]fluorenes via dihydronaphthalenes. The presence of a selenium electrophile and a Lewis acid are crucial for the formation of the C? C bonds.