Sultams elimination reactions

P-Sultams.1 Reaction of 1 with imines and a base (usually pyridine) in THF results in 4-carbomethoxy-l,2-thiazetidine 1,1-dioxides (2) in 20-93% yield. All products have the trans-orientation. The N-unsubstituted P-sultams can be obtained by use of phenylselenenylethyl as the R group. This R group can be replaced by hydrogen in 70-90% yield by selenoxide elimination to an enamide, which is then treated with I2 and Na2S03.2... 

Sultams like (190) undergo aminolysis with amines by nitrogen-sulfur bond cleavage (similar to hydrolysis), and suitably functionalised sultams (191) may also suffer carbon-nitrogen bond cleavage by a bimolecular (E2) elimination reaction (Scheme 79). 

Oppolzer et al. (321) applied his own sultam as the auxiliary for a cychc nitrone in the synthesis of (—)-allosedamine (Scheme 12.60). The enantiomerically pure nitrone 209 was synthesized from 208 by base treatment, attack of the enolate on 1-chloro-l-nitrosocyclohexane at the nitrogen atom, and subsequent elimination of chloride. Subsequent addition of aqueous HCl gave the cyclic nitrone 209. The nitrone participated in a 1,3-dipolar cycloaddition with styrene, proceeding with complete exo-specificity. The product, 210, was obtained with a de of 93%. Two further reaction steps yield the piperidine alkaloid ( )-aUosedamine 211 in an overall yield of 21%. 

It should be noted that if a 4,4-disubstituted /3-sultam is submitted to a desilylation reaction, decomposition is observed (Equation 7). This can be explained by fluoride-catalyzed desilylation followed by fluoride-catalyzed sulfur dioxide extrusion and elimination of hydrazine-1,2-dicarboxylate <2004HCA1574>. 

The availability of C-3-functionalized /3-sultams provides an opportunity to synthesize bicyclic derivatives in a straightforward manner (Scheme 37). The controlled addition of methylmagnesium bromide to ester 117 gave rise to a chromatographically separable mixture of ketone 118 and alcohol 119. Independent conversion to diene 120 was carried out via Wittig reaction from 118 or elimination using phosphorus oxychloride in pyridine from... 

In view of their importance in enantioselective reactions, many bornane sultams have been synthesized and characterized by MS. Their El mass spectra show molecular ions with low abundance or are absent. N-Substituted bornane sultams generally show the typical fragmentations of the substituents <2000THS(4)405>. 1-Alkyl-7-nitro-2,1-benzisothiazole 2,2-dioxides show elimination of an acyl radical from their molecular ions <1997EJS55>. 

The interaction of 4-alkyl-5-arylimino-l,2,3,4-thiatriazoline (69) and sulfenes (generated in situ from alkylsulfonyl chlorides and triethylamine82) produces sultams (72), possibly by way of the heteropentalenes (71) these isomerize above 60°C under the influence of acidic catalysts to 73, by a Dimroth rearrangement.77 The sultams (72) are themselves capable of acting as masked 1,3-dipoles, undergoing cycloaddition with heterocumulenes, with elimination of the sulfene moiety. Thus reaction of 72 with phenyl isocyanate produces the 1,2,4-thiadiazolidine (70), also directly accessible from 69 by Path A.83... 

The benzyne created from 2-(trimethylsilyl)phenyl triflate was used in a highly diastereoselective aiyne Diels-Alder reaction with a diene bearing Oppolzer s sultam. This approach to cis-functionalized 1,4-dihydronaphthalenes was reportedly the first aryne Diels-Alder reaction to provide enantioenriched cyclo-adducts. An unusual route to /3-aminoketones involves the treatment of 2-(trimethylsilyl)phenyl triflate with TBAF and an asymmetric vinyldihydropyridone. The resultant aryne Diels-Alder cycloadduct undergoes aromatization/elimination to create the A -acyl-/3-aminoketone (eq 13). This method was featured in a multistep synthesis of an unnatural a-amino acid. 

Chiral a-unsubstituted a,)8-unsaturated, isotopically carbon-labeled imides or esters (such as 249 above) needed as starting materials for such applications are best prepared by Horner-Wadsworth-Emmons reaction of e.p. (7 )-or-(5)-A-diethylphosphonoacetyl 4-substituted l,3-oxazolidin-2-ones or bornane-10,2-sultams or of (1R,2S,3R)/ (15,2R,35)-3-[A-phenylsulfonyl-A-(3,5-dimethylphenyl)amino]bornyldiefhylphosphono-acetates (e.g., 252) with aldehydes For purposes of isotopic synthesis, labels could be incorporated either via the haloacetyl group or the aldehyde component, or both, as suggested in Figure 11.87. Entities of the 249-type are also accessible through aldol reaction of the respective homochiral acetyl derivatives 253 with aldehydes, (9-acetylation of the resultant diastereomeric )8-hydroxy intermediates 254 and elimination of HO Ac upon treatment with Both methods avoid the separate preparation of labeled... 

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