Organotin hydrides reactions

Organotin Hydrides, Reactions with Organic Compounds, 1, 47... 

In contrast to the organotin hydride reactions, the electrochemical process is thought to proceed via the bicyclo[3.1.0]hexanolate. The method constitutes an alternative methodology which avoids toxic organotin compounds. 

Organotin hydride Reaction of iodooctane, followed by glc detn. of octane formed Weinshenker a/., 1975... 

By the addition of organotin hydrides to norbomene and norboma-diene, and subsequent reactions of the products, a variety of nor-bomyl-, norbornenyl-, and nortricyclyl-tin compounds has been isolated, and identified (67-69). 

The propensity of organotin hydrides for SET reactions has been utilized to initiate radical chain reactions. Anodically promoted oxidation of Ph3SnH to [Ph3Sn] at 0.80 V (vs SCE) initiates the cyclization of several haloalkyne and haloalkene ethers as well as of some fi-lactam derivatives. The catalytic cycle shown in Scheme 1 is based on... 

Many other groups can be selectively reduced by organotin hydrides. Although these reactions have not been used to date to form labelled compounds, the reactions are included here using tributyltin deuteride as the reducing agent to illustrate the synthetic possibilities for this reagent. 

Although these groups can be reduced with organotin hydrides, John and coworkers78 found that cyclic products accompanied the reduced (hydrocarbon) products in some reactions see Schemes 16 and 17 (vide supra). 

All of these syntheses begin with the addition of an organotin hydride to a carbon-carbon it bond. Therefore, it is important to understand the scope of these addition reactions. Organotin hydrides add without initiators to olefinic bonds, which are activated with an electron-withdrawing group. The hydride of the organotin hydride always adds to the more positive carbon in the addition reaction (equation 87). 

Organotin hydrides can also be added to unactivated olefinic (without an electron-withdrawing group on one carbon) bonds provided the reaction is initiated by UV radiation, AIBN or y-rays113-116. In one instance, an organotin hydride has even been added to an unactivated olefin without an initiator. This unexpected addition reaction occurred at high pressure117. 

The trialkylstannyl intermediates required in this synthetic sceme to prepare labelled compounds can be obtained in several ways. One method is the addition of the organotin hydride to the carbon-carbon triple bond of an alkyne (equation 93). These reactions have already been discussed in detail above. A second approach is to add a trialkylstan-nylvinyllithium to a ketone (equation 95), and a third method involves adding trialkylstan-nyllithium to a /J-halo, a, /J-unsaturated ester (equation 96). Although this last reaction gives a suitable trialkylstannane, these stannanes have proven to be inert in the destanny-lation reaction and, therefore, have not been used extensively to prepare radiolabelled compounds. 

The dehalogenation of organic halides by organotin hydrides takes place in most cases with a free-radical mechanism [1, 84, 85], The stereospecific reduction of 1,1-dibromo-l-alkenes with Bu3SnH discovered by Uenishi and coworkers [86-89], however, did not occur in the absence of palladium complexes and did not involve radicals. For the synthesis of (Z)-l-bromo-l-alkenes, [(PPh3)4Pd] proved to be the most effective catalyst which could also be generated in situ. The reaction in Eq. (7) proceeded at room temperature and a wide range of solvents could be used. 

The formation of rings with more than seven atoms has unfavorable rates because the addition step is often too slow to allow it to compete successfully with other pathways open to the radical intermediate. In stannane based chemistry for example, premature hydrogen abstraction from the organotin hydride is difficult to avoid. However, Baylis-Hillman adducts 111 derived from enantiopure 1-alkenyl (or alkynyl)-4-azetidinone-2-carbaldehydes are used for the stereoselective and divergent preparation of highly functionalized bicycles 112 and 113 fused to medium-sized heterocycles (Scheme 38) [80, 81]. The Baylis-Hillman reaction using nonracemic protected a-amino aldehydes has been attempted with limited success due to partial racemization of the chiral aldehyde by DABCO after... 

Diene-Iron Carbonyl Complexes and Related Species R. Pettit and G. F. Emerson Reactions of Organotin Hydrides with Organic Compounds Henry C. Kuivila Organic Substituted Cyclosilanes... 

FIGURE 27.1 Diastereotopic transition states involved in the reaction of a prochiral carbon-centered radical with a chiral organotin hydride. 

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