Dimethyl adduct with iodine

Similarly, alkenyllithium reagents add to dimethyl boronate to give adducts that decompose to Z-alkenes on treatment with iodine.27... 

Interestingly, the introduction of two bromomethyl functions in 4- and 5-positions of ethylen-l,3-dithiole-2-thione leads to a packing determined by weak interactions involving also the bromine atoms. One I2 molecule behaves as an acceptor towards S and as donor towards the second I2 molecule, which in turn behaves as donor towards the a c Br orbital (Figure 13). Intermolecu-lar S- -Br, CFF Br and L -I contacts make up a three-dimensional network.480 Reaction of 5,5-dimethyl-2-selenoxoimidazoline-4-one with iodine provided the first structurally characterised compound of the type [RR C Se — I-I].32 The Se-I bond is shorter (269.9 pm) and the I-I contacts are longer (296.2 pm) than in 1 1 adducts of dialkylselenides with iodine (see Chapter 8.2). 

The methanol extract of the sponge Haliclona vansoesti is toxic to brine shrimp. The extract was chromatographed and the main component isolated. The compound was determined to have the two-dimensional structure shown (R = H) after analysis of the IR and 1-D NMR data. The compound was converted to the triacetate (R = Ac) followed by reaction of a small amount (0.3 mg) of the triacetate with dimethyl disulfide and iodine. GC-MS analysis of the resulting adduct showed a molecular ion at m/z = 463 and fragment ions at m/z = 145 and 318. Determine the exact position of the double bond in this natural product. 

In a similar reaction, vinyllithium reagents add to dimethyl borinates (dimethoxyboranes) to give adducts which decompose to alkenes on treatment with iodine. 

Scheme 8.13 and Eqs. 8.6-8.10 reveal that lithiated methoxyallene 42 is sufficiently reactive towards a variety of electrophiles such as alkyl halides [44, 45], ethylene oxide [12c], tosylated aziridine 45 [46], dimethyl disulfide [12b], trialkylstannyl and trialkylsilyl chlorides [47, 48] and iodine [49]. These substitution reactions proceed with excellent regioselectivity and the corresponding a-functionalized products are obtained in good to high yields. An exceptional case was found by treatment of 42 with a guanidinium salt, which led to a 60 40 mixture of a- and y-adducts 50 and 51 (Eq. 8.11) [50],... 

Dimethyldisulfide derivatization is the most common method used for double bond position determination. Reaction of the alkene in hexane with dimethyl disulfide (DMDS) and iodine under an inert atmosphere at 60°C produces the DMDS adduct. MS fragmentation of the DMDS derivatives occurs between the methylsulfide groups, thus locating the original double bond position (Figure 7). DMDS derivatization was used for the determination of the double bond position in (E)-8-dodecenyl acetate, the sex pheromone of the citrus fruit borer. 

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