In the presence of catalytic amounts of dichlorobis(triphenylphosphine)palladium or of the x-allylmolybdenum complex 3, tributyltin hydride adds instantaneously at room temperature to various alkynes to give the corresponding vinylstannanes in good to excellent yields. The reaction is totally stereoselective (cis addition). With monoalkylacetylenes RC=CH, good regioselectivity for the formation of l-(tributylstannyl)alkenes (vs 2-(tributylstannyl)alkenes) is attained only if the R substituent is sufficiently bulky. The molybdenum-catalyzed hydrostannation of (trimethylsilyl)acetylene gives l-(tributylstannyl)-l-(trimethylsilyl)ethene with 85% selectivity. The palladium-catalyzed hydrostannation of 1-chloro-l-octyne regio-and stereoselectively yields (E)-l-chlorol-(tributylstannyl)octene, which, on reaction with I2 or Br2, leads to the corresponding 1-chloro-l-halo-l-octenes with total conservation of stereochemistry. 1-Bromo-l-alkynes behave differently from their chloro analoguers, reacting with 2 equiv of tributyltin hydride to give (£)-l-(tributylstannyl)-l-alkenes. Conjugated alkynones or alkynoic esters generally yield (E)-a-(tributylstannyl)enones and enoates esters which are important synthons in organic chemistry. Symmetrically substituted internal conjugated diynes, 1,3-diynes and l-(trimethylsilyl)-l,3-diynes give a single monohydrostannation product with total chemo-, regio-, and stereoselectivity.

In addition to being a powerful tool in synthetic organic chemistry, the palladium-catalyzed allylic alkylation reaction (the Tsuji-Trost reaction) has increased the use of allylic groups in protective group chemistry by offering a new general method for deprotection. Of the allylic protecting groups, the allyl group (All) and the allyloxycarbonyl group (Alloc) are the most commonly employed, the former for the protection, inter alia, of carboxylic acids, phosphoric acids, or phenols, and the latter for the protection of alcohols and amines. For the palladiumcatalyzed removal of these groups (eqs 1 and 2), various Y -C O z H + NuH (or NU' then H+) pd c a P ' Y * '~ YH + COZ + Nunucleophilic species (Nu-, NuH) have been used as allyl group scavengers, including oxygen, nitrogen, and carbon nucleophiles, as well as hydride donors' (formic acid and tributyltin hydride).We report herein that N,"-dimethylbarbituric acid (NDMBA, 71, a carbonnucleophile first proposed by Kunz and Miirz2 for the deprotection of Alloc derivatives of amines (eq 21, is also a very efficient allyl group scavenger in the palladium-catalyzed deallylation of mono-and diallylamines (eq 1, Z = NR2). To the best of our knowledge, this deprotection constitutes the first example of a deprotection of allyl derivatives of amines based on T-allyl method~logy.~ (1) Merzouk, A.; Guib4, F.; Loffet, A. Tetrahedron Lett. 1992,33,477 and references cited therein. (2) (a) Kunz, H.; M b , J. Angew. Chem.,Znt. Ed. Engl. 1988,27,1375. (b) Bratln, P.; Waldmann, H.; Vogt, W.; Kunz, H. Synlett 1990,105. (3) Previously published methods for the deallylation of allylamines involve isomerization to enamines either with potassium tert-butoxide (Montgomery, J. A.; Thomas, H. J. J. Org. Chem. 1965,30,3236) or by transition metal (Pd, Rh, Ir) catalysis. The f i t method involves rather harsh conditions, and, in the second one, careful choice of the catalyst and of the reaction conditions must be exercised to avoid poisoning of the catalyst, competitive reduction of the allyl group to a propyl group, and other side reactions; we for instance: Moreau, B.; Lavielle, S.; Marquet, A. Tetrahedron Lett. 1977,2591. Sundberg, R. J.; Hamilton, G. 5.; Laurino, P . J. J. Org. Chem. 1988,53, 976. See also ref 6. The deallylation of allylamines with carbonochloridate reagents (Kapnay, H.; Charles, G. Y . Tetrahedron Lett. 1983,3233) and, very recently, anth a zirconocene species generated in situ (Ito, H.; Taguchi, T.; Hanzawa, Y . J. Org. Chem. 1993,58, 774) have also been reported. 0022-3263/93/1958-6109$04.00/0Table I. Deprotmtion of Allylamines by the Palladium Catalyst/NDMBA System ~~ ~~ product! temp reactn entry substrate ("C) time (h) (isolated yield (%)) 1.5 N / 30 1 PhCH2NV\\ 1 2 3 (Ph)&HNH I 4 % 35 2 "CHICooEt 4 5 6 -NCHCOdPr 35 2 (iH&SCH3 6 PhCHzNHz (100) PhCH, PhCHzNNH (%)HzNCHZCOOEt (92) a Isolated as their hydrochloride salta.We found that N-allyl derivatives of primary or secondary amines such as N,N-diallylbenzylamine (11, Nallylbenzhydrylamine (21, or N-allyldibenzyla...

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