Since its inception, click chemistry has been established as a powerful approach for molecule synthesis. Strategies within click chemistry include several widely used reactions such as the (hetero-)Diels-Alder, 1,2 alkene hydrothiolation, and an array of amide-bond forming chemistries. However, by virtue of the access to alkyne and azide precursors and the formation of a single 1,4-disubstituted triazole product, the copper-catalysed azide-alkyne cycloaddition (CuAAC) remains the archetypal click reaction (Scheme 1). Scheme 1. The CuAAC reaction and installation of functional groups for product diversification. The reaction has shown applicability on small and large scale, as well as under flow conditions, and extensive scope across a range of benign solvent conditions. In addition, the CuAAC reaction uses inexpensive Cu catalysts, 11 is insensitive towards oxygen and water, and consistently delivers high yields and (where relevant) enantioselectivities. As such, the reaction has been used extensively throughout drug discovery, chemical biology, and materials science. Orthogonal alkyne reactivity can also be observed under certain systems. The reaction typically uses a Cu(II) pre-catalyst, which is converted to a mechanistically-required Cu(I) species in situ through the addition of a reductant (e.g., sodium ascorbate, NaAsc), or via Glaser-Hay alkyne homocoupling. The mild and accessible nature of the CuAAC reaction has allowed the use of azide or alkyne components that bear functional groups for subsequent product diversification (Scheme 1). For example, protected alkynylboron reagents can be employed, such as N-methyliminodiacetic acid (MIDA), potassium trifluoroborates, and others. Similarly, organosilicon reagents have proven useful in various Cu-and Pd-catalysed C-X bond forming strategies, including widespread use across several CuAAC methodologies. Germanium-based functional groups have recently emerged as highly useful components for transition metal-catalysed crosscouplings. Schoenebeck and co-workers have shown that Gebased compounds are versatile reagents for chemoselective cross-coupling processes for the formation of a variety of C-C and C-X bonds. Importantly, these transformations can take place in the presence of borylated functional groups, allowing orthogonal cross-coupling, whilst also offering excellent stability compared to boron-based reagents. Based on their utility and stability, germanium units could therefore be useful within CuAAC reactions and offer potential as functional handles for downstream elaboration of CuAAC products. To date, the use of germanyl alkynes in (3+2) cycloadditions has been limited to a small number of Huisgen (non-Cu-catalysed) reactions. Here we report the development of germanyl alkynes as CuAAC components, with exploration of their scope and downstream diversification. We undertook an exploratory survey of CuAAC reaction conditions using benzyl azide and triethylgermanyl acetylene (see ESI). The most effective conditions were found to be based on the classical combination of CuSO4/NaAsc, with optimisation (see ESI) delivering the general conditions shown in Scheme 2. These afforded clean conversion to the desired triazole products (1-21) without any observable degermylation or other side reactions that could be anticipated based on transmetalation to Cu. The generality of the CuAAC process was explored using a range of azides (Scheme 2a), with variation of the germanyl alkyne motif (Scheme 2b), and with variation of both components (Scheme 2c). In general, the CuAAC process worked effectively, tolerating the functional groups for which the CuAAC is wellknown -in all cases the remaining mass balance was the germanyl acetylene, suggesting sluggish CuAAC reactivity compared to other alkynes, which typically require much shorter reaction times. Extending the reaction time provided higher conversion to the product (14). Yields were observed to be greater for aryl azides (e.g., 4 vs. 6). Heterocycles such as pyridine (1), pyrimidine (10), phenothiazine (11), and chromene (12) were tolerated. Benzylic azides were accommodated including those bearing nitro (2), iodo (3), and boronic ester groups (5, 21). Strained rings were effective including cubane (18) and bicyclopentane (20). While 18 and 20 were isolated in lower yield, no evidence of ring opening was observed and the starting material could be recovered in each case, consistent with observations by MacMillan. Variation of the steric and electronic parameters of the germanyl acetylene was straightforward (14-17; Scheme 2b). Several limitations were observed (Scheme 2d): benzyl azides displaying an arylboronic acid and MIDA ester (22 and 23) gave no reaction, side reactions were observed with a dialkynyl germane (24), and the product derived from azide 25 was unstable to purification.