The possibilities of additions to the activated CC triple bond are discussed with the aid of a number of examples. The additions of donors that contain no active hydrogen are generally initiated via a dipolar primary complex, which can undergo stabilization by rearrangement, cyclization, or addition reactions. Preparative aspects of these reactions are also discussed. They offer routes for the preparation of heterocycles, particularly pyrrole and thiophene derivatives.

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The structure of product (8) follows from its cleavage by acid to cyclohexanone (2,4-dinitrophenylhydrazone, m.p. 162 "C) and 4-phenylsemicarbazide (benzylidene derivative, m. p. and mixed n1.p. 180°C).

p-l.~othioc~nnatobenzei~es~r/fonyl isocyaitttte ( I ) :Phosgenz is passed (1 gjmin; 90 min) into a boiling solution of p-isothiocyanatobenzenesulfonamide~2~ (21.4 g, 0.1 mole) and n-butyl isocyanate (8.56 g) in o-dichlorobenzene (500 ml).Nitrogen is passed through the mixture, and then the solvent and catalyst are removed in a vacuum. Vacuum-distillation of the residue gives 19 g (79%) of p-isothiocyanatobenzenesulfonyl isocyanate, b.p. 140 "CiO.2 mm, m.p. 64-67 OC; IR, h:::13 .= 2232 cm-1 (NCO) and 2128-2041 cm-1 (NCS).