Hydrostannation allenes

Sequential hydrostannation-palladium catalysed cyclisation of the allene 56 leads to formation of the vinyltetrahydobenzoxazepine 57 <96T13441>. 

Hydrostannation of (l-alkynyl)carbene chromium complexes involves addition to the M = C bond as well as to the C=C bond and is strongly influenced by the substituent at the alkynyl moiety. By the bulky trimethyl-silyl group of compound lg, a 1,1-addition to the carbene carbon atom is promoted with formation of a densely functionalized 1,3-heterobimetal lie propargyl reagent 93 containing both a stannyl and a silyl group. A 3,1-addition is observed with phenyl derivative la and also the vinyl compound lo, which leads to production of an allene 94 and 95, respectively (Scheme 31).111... 

Hydrostannation of 1-alkynes does provide vinyltins (equation 29), but these reactions may not be stereospecific or give the desired regiospecificity. Other methods from aUcynes are shown in equations 30 and 31 and Scheme 6. Stannyl cupration of allenes (using (Bus Sn)2CuLi or (Bus Sn)BuCuLi) also leads to allyl- and vinylstannanes. ... 

This section deals mainly with the hydrostannation of alkenes, and further details can be found in the appropriate subsequent sections on, for example, stannyl radicals (Section 20.1.3), and stannacycloalkanes (Chapter 10). The hydrostannation of alkynes, allyl compounds, and allenes, is dealt with in Sections 8.1.1 and 10.1. which cover the vinyl-and allyl-tin compounds which are produced. 

Acetylenes and allenes can also be smoothly hydrostannated under these conditions 444 for example, tributyltin hydride and acetylene give tributyl-(vinyl)tin in very good yield.445 Conjugated dienes afford mainly the 1,4-adducts.446... 

Allenyltins are conveniently prepared from the terminal alkynes which have a suitable leaving group. An example is shown in equation 19. A two-step one-pot procedure for the synthesis of allene by hydrostannation of alkynes has recently been reported starting from propargylic alcohols a hydrostannation and subsequent deoxystannylation generates the allenes 6 as shown in equation 20. A chiral version of this procedure has also been described in the paper. 

RXN17 Hydroboration, Hydrogermylation, Hydrosilylation and Hydrostannation of Alkynes, Allenes, Dienes and Enynes... 

Aside from the Pd-catalyzed hydrosilation of allene itself shown in Scheme 4, few additional examples of Pd-catalyzed hydrosilation of allenes appear to have been reported, even though the corresponding hydrostannation has extensively been investigated, as detailed in Sect. C. 

Only a small number of investigations of Pd-catalyzed hydrostannation of allenes have been reported. In 1988, Oshima and co-workers reported what appears to be the first investigation of this topic together with a related study of hydrogermation (Scheme 28). 

A more recent smdy has shown that the Pd-catalyzed hydrostannation of terminal allenes can and does indeed produce aU of the six readily conceivable products shown in... 

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