Eric J. Roskamp

Tin(II) chloride catalyzed addition of diazo sulfones, diazo phosphine oxides, and diazo phosphonates to aldehydes.

Abstract Diazo sulfones, diazo phosphine oxides, and diazo phosphonates add to aldehydes in the presence of a catalytic amounts of tin(II) chloride to yield β-keto sulfones, β-keto phosphine oxides, and β-keto phosphonates, respectively. Reactions with primary aldehydes proceed in higher yields, 53–79%, than those of secondary aldehydes, 42–56%. Reactions with tertiary aldehydes, which are more sterically encumbered substrates, give only 5–36% yields.

The conversion of carboxylic acids to amides via tin(II) reagents

Abstract Unsymmetrical tin(II) amides can be generated, in situ, by adding one equivalent of an amine to bis(bistrimethylsilylamino) tin, Sn[N(TMS)2]2. Treatment of carboxylic acids with these tin(II) reagents derived from alkyl or aryl amines results in smooth conversion to the corresponding N-alkyl or N-aryl amides.

Tin(II) chloride dihydrate: A mild and efficient reagent for cleaving acetals.

Abstract Tin(II) chloride dihydrate (SnCl2·2H2O) efficiently converts conjugated dioxolones, and both dimethoxy and diethoxy acetals to aldehydes (84–98%). Similarly, nonconjugated dimethoxy and diethoxy acetals are also efficiently converted to aldehydes (84–94%). Conjugated pyrans and nonconjugated dioxolanes, however, are only converted to aldehydes in 17–38% yields.

New technology for the construction of bicyclo [6.2.1] ring systems

Abstract Three new methods are presented in this synthesis of an 11-oxabicyclo[6.2.1]-undec-1,5,9-triene. They include: (1) the preparation of the dianion of 3-hydroxy-1,4-pentadiene; (2) an intramolecular Diels-Alder reaction accelerated by silica gel saturated with water; and (3) a tandem Grob fragmentation and homoallylic elimination of a cyclic sulfate. Overall, the synthesis of (1 E , 5 E , 9 Z )-2-(t-Butyldimethylsiloxy)-8-methyl-11-oxabicyclo[6.2.1]-undec-1,5,9-triene ( 1 ) was completed in 9 steps starting from 5-methylfurfural.

Direct conversion of esters to secondary amides using Tin(II) reagents

Abstract We have developed two new procedures for the direct conversion of esters to secondary amides. In our first procedure, secondary amides can be prepared in 83–98% yield starting from glycol esters. Addition of Sn[N(TMS) 2 ] 2 and a primary amine to the glycol ester generates an intermediate tin(II) alkoxy amide, which delivers the amino group intramolecularly to give the amide. A second general procedure for the preparation of secondary amides start with methyl esters. Treatment of methyl ester with a tin reagent derived from Sn[N(TMS) 2 ] 2 , Me 2 NCH 2 CH 2 OH, and a primary amides in 87–98% yield.

The conversion of olefins to β-keto esters: Ozonolysis of olefins followed by in situ reduction with tin(II) chloride in the presence of ethyl diazoacetate.

Abstract Trisubstituted olefins are converted to β-keto esters by treatment with ozone followed by the addition of tin(H) chloride and ethyl diazoacetate. Monosubstituted olefins are first treated with ozone in the presence of methanol to generate methoxy hydroperoxides. The hydroperoxides are subsequently reduced with tin(II) chloride in the presence of ethyl diazoacetate to produce β-keto esters.