Sulfonyl-amino-alkenes, with

A related cyclization of N-sulfonyl-amino-alkenes and NBS gave the bromo-lactam, " and a dichloro-Af,7/-bisallylamide was converted to a dichloro-lactam with FeCl2. ... 

An intramolecular allyl silane/N-sulfonyl iminium ion cyclization has also been used as a pivotal step in an approach to the tricyclic core of the unique marine alkaloid sarain A [46]. The starting material was aziridine ester 129 (Scheme 25) which was elaborated to amide 130. An important step in the synthetic strategy was thermolysis of 130 to an azomethine ylide, which underwent stereospecific intramolecular 1,3-dipolar cycloaddition with the Z-alkene to produce bicyclic lactam 131 [47]. This compound was then elaborated into allyl silane 132. It was then possible to replace the lactam N-benzyl functionality with a tosyl moiety, leading to 133, and subsequent reduction of the carbonyl group afforded the desired cyclization precursor a-hydroxy sulfonamide 134. Exposure of 134 to ferric chloride promoted cyclization to a single stereoisomeric tricyclic amino alkene 136 having the requisite sarain A nucleus. It is believed that the intermediate N-sulfonyl iminium ion cyclizes via the conformation shown in 135. 

Several thiols occur naturally for example, skunk secretion contains 3-methyll-butanethiol and cut onions evolve 1-propanethiol, and the thiol group of the natural amino acid cysteine plays a vital role in the biochemistry of proteins and enzymes (see Introduction, p. 2). Primary and secondary thiols may be prepared from alkyl halides (RX) by reaction with excess sodium thiolate (SN2 nucleophilic substitution by HST) or via the Grignard reagent and reaction with sulfur. Tertiary thiols can be obtained in good yields by addition of hydrogen sulfide to a suitable alkene. Thiols can also be prepared by reduction of sulfonyl chlorides (Scheme l).la,2a... 

Just as alkenes can be condensed with isocyanates, one alkene unit of a diene can also react, eventually leading to an alkenyl amino acid. The condensation of CSI and 1,3-pentadiene in reaction 4 is one example and it gave 2.J02.51 Removal of the sulfonyl group and hydrolysis gave methyl 3-aminohex-4-enoate (2.55),51c a synthetic intermediate for the preparation of daunosamine.51a.c Similar reaction with 1,3-... 

A variety of functionalized alkenes has been directly obtained with E selectivity from the Homer-Wittig reaction of aldehydes (or ketones) with phosphine oxide-stabilized carbanions bearing in the a position certain functional groups such as aryl [197], vinyl [198-200], cyano [201], sulfonyl [202], isoxazole [203], amino [204], or alkylthio [205]. The functional group provides stabilization for the negative charge of the p-oxido phosphine oxide intermediate and lowers the activation energy for the elimination step to form an alkene (Scheme 42). 

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